U.S. patent number 8,795,933 [Application Number 12/910,397] was granted by the patent office on 2014-08-05 for electrophotographic photoconductor, method for preparing the same, process cartridge, and image forming apparatus.
This patent grant is currently assigned to Fuji Xerox Co., Ltd.. The grantee listed for this patent is Takatsugu Doi, Yuko Iwadate, Katsumi Nukada, Wataru Yamada. Invention is credited to Takatsugu Doi, Yuko Iwadate, Katsumi Nukada, Wataru Yamada.
United States Patent |
8,795,933 |
Doi , et al. |
August 5, 2014 |
Electrophotographic photoconductor, method for preparing the same,
process cartridge, and image forming apparatus
Abstract
An electrophotographic photoconductor includes a conductive
substrate and an outermost surface layer on the conductive
substrate. The outermost surface layer contains a copolymer (a)
derived from a reactive monomer having charge transport property
and a reactive monomer having no charge transport property, and a
polymer prepared by polymerizing, in the presence of the copolymer
(a), a reactive monomer (b) that has a solubility parameter (SP
value) different from a solubility parameter (SP value) of the
reactive monomer having no charge transport property by about 2
(cal/cm.sup.3).sup.1/2 or less.
Inventors: |
Doi; Takatsugu (Kanagawa,
JP), Yamada; Wataru (Kanagawa, JP),
Iwadate; Yuko (Kanagawa, JP), Nukada; Katsumi
(Kanagawa, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
Doi; Takatsugu
Yamada; Wataru
Iwadate; Yuko
Nukada; Katsumi |
Kanagawa
Kanagawa
Kanagawa
Kanagawa |
N/A
N/A
N/A
N/A |
JP
JP
JP
JP |
|
|
Assignee: |
Fuji Xerox Co., Ltd. (Tokyo,
JP)
|
Family
ID: |
45352865 |
Appl.
No.: |
12/910,397 |
Filed: |
October 22, 2010 |
Prior Publication Data
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|
|
|
Document
Identifier |
Publication Date |
|
US 20110318676 A1 |
Dec 29, 2011 |
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Foreign Application Priority Data
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Jun 28, 2010 [JP] |
|
|
2010-146982 |
|
Current U.S.
Class: |
430/58.7; 430/56;
430/50 |
Current CPC
Class: |
G03G
5/14708 (20130101); G03G 5/0614 (20130101); G03G
5/0596 (20130101); G03G 15/751 (20130101); G03G
5/0525 (20130101); G03G 5/0532 (20130101); G03G
5/0592 (20130101); G03G 5/071 (20130101) |
Current International
Class: |
G03G
15/00 (20060101) |
Field of
Search: |
;430/56,58.65,60,64,50,58.7 |
References Cited
[Referenced By]
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101174112 |
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101539727 |
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101607490 |
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A-05-331238 |
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B2-3287678 |
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A-2004-012986 |
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JP |
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A-2004-302450 |
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A-2006-084711 |
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Mar 2006 |
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Other References
Dec. 16, 2013 Chinese Office Action issued in Chinese Patent
Application No. CN 201010590777.X (with English-language
Translation). cited by applicant.
|
Primary Examiner: Huff; Mark F
Assistant Examiner: Alam; Rashid
Attorney, Agent or Firm: Oliff PLC
Claims
What is claimed is:
1. An electrophotographic photoconductor comprising: a conductive
substrate; and an outermost surface layer on the conductive
substrate, the outermost surface layer containing a copolymer (a)
that includes a constitutional unit represented by general formula
(1) below derived from a reactive monomer having charge transport
property and a constitutional unit represented by general formula
(2) below derived from a reactive monomer having no charge
transport property: ##STR00118## where, in general formulae (1) and
(2), R represents an organic group having no charge transport
property; R.sup.1 and R.sup.2 each independently represent hydrogen
or an alkyl group having 1 to 4 carbon atoms; X represents a
divalent organic group having 1 to 10 carbon atoms; a represents 0
or 1; and CT represents an organic group having a charge transport
skeleton, and a polymer prepared by polymerizing, in the presence
of the copolymer (a), a reactive monomer (b) that has a solubility
parameter (SP value) different from a solubility parameter (SP
value) of the reactive monomer having no charge transport property
by about 2 (cal/cm.sup.3).sup.1/2 or less, wherein a ratio of a
constitutional unit derived from the reactive monomer having no
charge transport property in the copolymer (a) is about 10 mass %
or less.
2. The electrophotographic photoconductor according to claim 1,
wherein the reactive monomer having no charge transport property
and constituting the copolymer (a) has the same structure as the
reactive monomer (b).
3. The electrophotographic photoconductor according to claim 1,
wherein both the reactive monomer having no charge transport
property and constituting the copolymer (a) and the reactive
monomer (b) have an alkylene oxide group.
4. The electrophotographic photoconductor according to claim 1,
wherein both the reactive monomer having no charge transport
property and constituting the copolymer (a) and the reactive
monomer (b) have a bisphenol skeleton.
5. The electrophotographic photoconductor according to claim 1,
wherein both the reactive monomer having no charge transport
property and constituting the copolymer (a) and the reactive
monomer (b) have an alkyl group having 6 or more carbon atoms.
6. The electrophotographic photoconductor according to claim 1,
wherein the reactive monomer having charge transport property and
constituting the copolymer (a) is a compound represented by general
formula (A) below: ##STR00119## where, in formula (A), Ar.sup.1 to
Ar.sup.4 may be the same or different and each independently
represent a substituted or unsubstituted aryl group; Ar.sup.5
represents a substituted or unsubstituted aryl group or a
substituted or unsubstituted arylene group; D represents a side
chain having a reactive group; c1 to c5 each independently
represent an integer of 0 to 2; k represents 0 or 1; and the total
number of D is 1 to 6.
7. The electrophotographic photoconductor according to claim 1,
wherein the reactive monomer (b) has two or more polymerizable
groups.
8. The electrophotographic photoconductor according to claim 1,
wherein the reactive monomer (b) is a compound represented by
general formula (B) below: ##STR00120## where, in formula (B),
Ar.sup.1 to Ar.sup.4 may be the same or different and each
independently represent a substituted or unsubstituted aryl group;
Ar.sup.5 represents a substituted or unsubstituted aryl group or a
substituted or unsubstituted arylene group; D represents a side
chain having a reactive group; c1 to c5 each independently
represent an integer of 0 to 2; k represents 0 or 1; and the total
number of D is 1 to 6.
9. The electrophotographic photoconductor according to claim 1,
wherein the outermost surface layer of a photosensitive layer
contains fluorine-based particles.
10. A method for preparing the electrophotographic photoconductor
according to claim 1, the method comprising: applying a coating
solution for forming an outermost surface layer of the
electrographic photoconductor onto the electrophotographic
photoconductor to form a coating layer, the coating solution
containing a copolymer (a) that includes a constitutional unit
represented by general formula (1) below derived from a reactive
monomer having charge transport property and a constitutional unit
represented by general formula (2) below derived from a reactive
monomer having no charge transport property: ##STR00121## where, in
general formulae (1) and (2), R represents an organic group having
no charge transport property; R.sup.1 and R.sup.2 each
independently represent hydrogen or an alkyl group having 1 to 4
carbon atoms; X represents a divalent organic group having 1 to 10
carbon atoms; a represents 0 or 1; and CT represents an organic
group having a charge transport skeleton, and a reactive monomer
(b) that has a solubility parameter (SP value) different from a
solubility parameter (SP value) of the reactive monomer having no
charge transport property by about 2 (cal/cm.sup.3).sup.1/2 or
less; and heating the coating layer of the coating solution applied
on the conductive substrate at an oxygen concentration of about
1000 ppm or less and a temperature of about 130.degree. C. or
higher.
11. The method according to claim 10, wherein the coating solution
contains a polymerization initiator.
12. The method according to claim 11, wherein the polymerization
initiator is a thermal polymerization initiator.
13. The method according to claim 12, wherein the thermal
polymerization initiator has a molecular weight of about 250 or
more.
14. A process cartridge comprising: the electrophotographic
photoconductor according to claim 1, wherein the process cartridge
is detachably attachable to an image forming apparatus.
15. An image forming apparatus comprising: the electrophotographic
photoconductor according to claim 1; a charging device that charges
the electrophotographic photoconductor; a latent image-forming
device that forms an electrostatic latent image on a surface of the
charged electrophotographic photoconductor; a developing device
that forms a toner image by developing the electrostatic latent
image formed on the surface of the electrophotographic
photoconductor with a toner; and a transfer device that transfers
the toner image formed on the surface of the electrophotographic
photoconductor onto a recording medium.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based on and claims priority under 35 USC 119
from Japanese Patent Application No. 2010-146982 filed Jun. 28,
2010.
BACKGROUND
(i) Technical Field
The present invention relates to an electrophotographic
photoconductor, a method for preparing the same, a process
cartridge, and an image forming apparatus.
(ii) Related Art
Electrophotographic photoconductors help achieve high print quality
and high printing rates and thus are widely used in the fields of
copy machines and laser beam printers. Currently, the mainstream of
the electrophotographic photoconductors used in such image forming
apparatuses is those that use organic photoconductive materials
which are superior to conventional electrophotographic
photoconductors that use inorganic photoconductive materials such
as selenium, selenium-tellurium alloy, selenium-arsenic alloy,
cadmium sulfide, or the like, in terms of cost, manufacturability,
and disposability.
Although a corona charging technique using a corona discharger has
been used as a charging technique, a contact charging technique
that generates less ozone and requires low power is increasingly
put into practical use. The contact charging technique involves
bringing a conductive member as a charging member into contact or
in close proximity with a surface of a photoconductor and applying
a voltage to the charging member to charge the surface of the
photoconductor. The voltage may be applied to the charging member
through a DC method by which only DC voltage is applied or through
an AC superimposition method by which AC voltage is superimposed on
DC voltage and applied. According to the contact charging
technique, the size of the apparatus is reduced and less toxic gas
such as ozone is generated. However, since direct discharge occurs
at the surface of the photoconductor, deterioration and wear of the
photoconductor tend to occur.
The mainstream of the transfer technique has been to directly
transfer images onto paper. However, recently, use of intermediate
transfer bodies has increased since the flexibility of choosing
paper onto which transfer is conducted is high.
SUMMARY
According to an aspect of the invention, there is provided an
electrophotographic photoconductor including a conductive substrate
and an outermost surface layer on the conductive substrate, the
outermost surface layer containing a copolymer (a) derived from a
reactive monomer having charge transport property and a reactive
monomer having no charge transport property, and a polymer prepared
by polymerizing, in the presence of the copolymer (a), a reactive
monomer (b) that has a solubility parameter (SP value) different
from a solubility parameter (SP value) of the reactive monomer
having no charge transport property by about 2
(cal/cm.sup.3).sup.1/2 or less.
BRIEF DESCRIPTION OF THE DRAWINGS
Exemplary embodiments of the present invention will be described in
detail based on the following figures, wherein:
FIG. 1 is a schematic partial cross-sectional view showing an
example of the layer configuration of an electrophotographic
photoconductor according to an exemplary embodiment;
FIG. 2 is a schematic partial cross-sectional view showing another
example of the layer configuration of an electrophotographic
photoconductor according to an exemplary embodiment;
FIG. 3 is a schematic diagram showing an example of a structure of
an image forming apparatus (process cartridge) according to an
exemplary embodiment;
FIG. 4 is a schematic diagram showing an example of a tandem-system
image forming apparatus according to an exemplary embodiment;
FIG. 5 is a diagram showing the standard for evaluation regarding
image deletion and white streaks; and
FIG. 6 is an IR spectrum of compound (I-14) synthesized in
Example.
DETAILED DESCRIPTION
Exemplary embodiments will now be described with reference to the
drawings. In the drawings, same or equivalent parts are referenced
by the same reference characters and the descriptions therefor are
omitted to avoid redundancy.
When a reactive charge transport material (low molecular weight)
and a (meth)acrylate or the like that does not have a charge
transport property are polymerized on a substrate to form a
photosensitive layer of a photoconductor and this photosensitive
layer is has a crosslinked structure, the photosensitive layer
presumably has many cross-linking points and forms a
three-dimensional network. Such a photoconductor tends to have poor
electrical characteristics although it has high mechanical
strength. Although the mechanism of deterioration of the electrical
characteristics is not clear, one of the possible causes may be the
deterioration of charge transport property by immobilization of
charge hopping sites caused by crosslinking. According to a
photoconductor prepared by polymerization on a substrate, the
polymerization reaction is generally conducted without any solvent.
Thus, presumably, the distance between the reactive group and the
charge transport skeleton is small, and side reactions between the
radicals generated on the reactive group and the electron transport
skeleton occur. As a result, presumably, the charge transport
property is degraded and this may be one of the causes for the
deterioration of the electrical characteristics.
The mechanical strength may be enhanced by preliminarily
polymerizing the charge transport material. However, in general,
when a polymeric transfer material is used, a one-dimensional
polymer is formed. Thus, in terms of crosslinking points, such a
polymer is poor compared to cured products of the (meth)acrylate
and the reactive charge transport material described above.
Accordingly, when a polymeric charge transport material is used,
the mechanical strength is low compared to when a cured product of
the reactive charge transport material and the (meth)acrylate is
used. However, the electrical characteristics tend to be better.
This is probably because charge hopping sites tend to remain
unrestrained.
Since it is difficult to obtain sufficient mechanical strength by
the characteristics of the polymeric charge transport material, the
polymeric charge transport material may be cured together with a
reactive acrylate to improve the mechanical strength. However,
since the two materials have low compatibility to each other, they
do not mix with each other homogeneously and it is difficult to
form a photoconductor. Moreover, the electrical characteristics may
deteriorate because of the low compatibility.
Under such circumstances, the inventors have continued studies and
found that when an electrophotographic photoconductor (may be
referred to as "photoconductor" hereinafter) that contains a
polymer obtained by polymerizing a reactive acrylate in the
presence of a polymeric charge transport material, the mechanical
strength is improved, the environmental dependency is suppressed
even when repeatedly used, and stable images is obtained. Further
studies have found that when a photosensitive layer, which is the
outermost surface layer, contains a copolymer (a) derived from a
reactive monomer having charge transport property and a reactive
monomer having no charge transport property (hereinafter this
copolymer is simply referred to as "copolymer (a)"), and a polymer
prepared by polymerizing, in the presence of the copolymer (a), a
reactive monomer (b) that has a solubility parameter (SP value)
different from the solubility parameter (SP value) of the reactive
monomer having no charge transport property, i.e., a constitutional
unit of the copolymer (a), by 2 (cal/cm.sup.3).sup.1/2 or less or
about 2 (cal/cm.sup.3).sup.1/2 or less, stable images are
obtained.
Note that the solubility parameter (SP value) of the reactive
monomer in this exemplary embodiment is a value calculated from the
equation of Fedors below based on the evaporation energy
(.DELTA.ei) and molar volume (.DELTA.vi) of the atoms or atomic
groups of the chemical structure: [SP
value=(.SIGMA..DELTA.ei/.SIGMA..DELTA.vi).sup.1/2] Equation
Although the mechanism therefor is not necessarily clear, the
following is presumed.
When the difference between the solubility parameter (SP value) of
the reactive monomer having no charge transport property, which is
a constitutional unit of the copolymer (a), and the solubility
parameter (SP value) of the reactive monomer (b) is 2
(cal/cm.sup.3).sup.1/2 or less or about 2 (cal/cm.sup.3).sup.1/2 or
less, the compatibility between the copolymer (a) and the reactive
monomer (b) is improved, and a photosensitive layer in which
separation of the copolymer (a) and the reactive monomer (b) is
suppressed is formed. As a result, presumably, while sufficient
mechanical strength is obtained by polymerizing the charge
transport material, the charge transport material becomes
sufficiently dispersed in the photosensitive layer, thereby
improving the electrical characteristics.
In contrast, when a polymeric charge transport material is prepared
in advance and polymerization between the polymeric charge
transport material and a reactive monomer is performed on a
substrate, the number of reactive groups involved in the
polymerization decreases during the polymerization on the
substrate. Thus, presumably, side reactions between the radicals on
the reactive groups and the electron transport skeleton is
suppressed, thereby improving the electrical characteristics.
The layer configuration of the electrophotographic photoconductor
used in this exemplary embodiment will now be described.
FIGS. 1 and 2 are schematic cross-sectional views showing examples
of the layer configuration of the electrophotographic
photoconductor of this exemplary embodiment. In FIG. 1, an
undercoat layer 1 is formed on a conductive substrate 4, and a
charge generation layer 2 and then charge transport layers 3A and
3B are formed on the undercoat layer 1. In the electrophotographic
photoconductor having this structure, the outermost surface layer
is the charge transport layer 3A.
In FIG. 2, an undercoat layer 1 is formed on a conductive substrate
4, and a charge generation layer 2 and then a charge transport
layer 3A are formed on the undercoat layer 1. In the
electrophotographic photoconductor having this structure, the
outermost surface layer is the charge transport layer 3A.
In the examples shown in FIGS. 1 and 2, the undercoat layer 1 may
be provided if necessary.
The individual layers will now be described by using the
electrophotographic photoconductor having a structure shown in FIG.
1 as a representative example.
<Charge Transport Layer 3A>
The charge transport layer 3A constituting the outermost surface
layer is first described. The charge transport layer 3A which
constitutes the outermost surface layer of the electrophotographic
photoconductor of this exemplary embodiment contains a copolymer
(a) derived from a reactive monomer having charge transport
property and a reactive monomer having no charge transport
property, and a polymer prepared by polymerizing, in the presence
of the copolymer (a), a reactive monomer (b) that has a solubility
parameter (SP value) different from the solubility parameter (SP
value) of the reactive monomer having no charge transport property,
i.e., a constitutional unit of the copolymer (a), by 2
(cal/cm.sup.3).sup.1/2 or less or about 2 (cal/cm.sup.3).sup.1/2 or
less. The charge transport layer 3A may contain other
materials.
In this exemplary embodiment, a monomer having two or more chain
polymerizable groups may be used as the reactive monomer (b). The
chain polymerizable groups may be functional groups including any
one of an acryl group, a methacryl group, a styryl group, and
derivatives thereof from the viewpoints of ease of synthesizing the
compounds and high reactivity. When polyfunctional monomers are
used, the compatibility between the copolymer (a) and the reactive
monomer (b) is high, and thus it is assumed that the resulting
structure has the copolymer (a) within the crosslinked structure of
the reactive monomer (b). Accordingly, it is presumed that the
synergy of the strength-improving effect achieved by the use of the
copolymer (a) and the strength-improving effect achieved by the
crosslinked structure of the polyfunctional reactive monomer (b)
further enhances mechanical strength.
In typical crosslinked photoconductors, the electrical
characteristics tend to be poor. However, molecules of the
copolymer (a) are allowed to move freely within the crosslinked
structure derived from the reactive monomer (b) and the degree of
freedom of hopping sites is enhanced. Moreover, it is assumed that
since the copolymer (a) is dispersed in the crosslinked structure
of the reactive monomer (b), sufficient electrical characteristics
are ensured.
The reactive monomer having no charge transport property, which is
a constitutional unit of the copolymer (a), may have the same
structure as the reactive monomer (b) from the viewpoint of the
compatibility between the copolymer (a) and the reactive monomer
(b). When monomers of the same structure are used, the effect of
improving both the mechanical strength and the electrical
characteristics is enhanced further.
When the reactive monomer (b) and the reactive monomer having no
charge transport property and constituting the copolymer (a) are
not of the same type, the effect of achieving both sufficient
mechanical strength and electrical characteristics are obtained if
both the reactive monomer (b) and the reactive monomer having no
charge transport property and constituting the copolymer (a) have
an alkylene oxide group, a bisphenol skeleton, or an alkyl group
having 6 or more carbon atoms.
In particular, when both monomers have an alkylene oxide group, not
only the compatibility between the monomers is improved but also
polymer entanglement is enhanced. Although both mechanical strength
and electrical characteristics are improved, incorporation of the
alkylene oxide group is particularly favorable in terms of
mechanical strength.
It is assumed that when both monomers have a bisphenol skeleton,
the compatibility between the monomers is enhanced and the
mechanical strength and electrical characteristics are
improved.
In particular, when both monomers have an alkyl group having 6 or
more carbon atoms, not only the compatibility between the monomers
is improved but also polymer entanglement is enhanced. In
particular, electrical characteristics are improved.
In this exemplary embodiment, the reactive monomer having no charge
transport property and being a constitutional unit of the copolymer
(a) may be a polyfunctional (meth)acrylate and the ratio of the
reactive monomer having no charge transport property may be 10 mass
% or less or about 10 mass % or less. This improves the mechanical
strength in particular. When a polyfunctional (meth)acrylate is
used, the number of cross-linking points increases and the
mechanical strength is improved. Moreover, because the ratio of the
reactive monomer having no charge transport property is 10 mass %
or less or about 10 mass % or less in the copolymer (a), sufficient
dissolution (dispersion) is maintained and deterioration of the
electrical characteristics is suppressed.
In this exemplary embodiment, the reactive group may be selected
from the group consisting of an acryl group, a methacryl group, a
styryl group, and derivatives thereof.
(Reactive Monomer Having Charge Transport Property)
The reactive monomer having charge transport property, which is a
constitutional unit of the copolymer (a) will now be described in
detail. In this exemplary embodiment, the "reactive monomer having
charge transport property" means a monomer having a charge mobility
of 1.times.10.sup.-10 cm.sup.2/Vs or more at a field intensity of
10 V/.mu.m measured by a time-of-flight (TOF) technique, and the
"reactive monomer having no charge transport property" means a
monomer having a charge mobility of less than 1.times.10.sup.-10
cm.sup.2/Vs under the same conditions.
The reactive monomers constituting the copolymer (a) may be any
material as long as it is a compound having both a reactive group
and an organic group having a charge transport skeleton within a
molecule.
Specific examples of the reactive monomer having charge transport
property used in this exemplary embodiment include monomers
represented by general formula (1-2) below:
##STR00001##
In general formula (1-2), R.sup.1 represents hydrogen or an alkyl
group having 1 to 4 carbon atoms, X represents a divalent organic
group having 1 to 10 carbon atoms, a represents 0 or 1, and CT
represents an organic group having a charge transport skeleton. X
may contain at least one substituent selected from the group
consisting of a carbonyl group, an ester group, and an aromatic
ring and may contain an alkyl group, preferably, an alkyl group
having 1 to 4 carbon atoms, in a side chain.
Compounds represented by general formula (A) below are more
preferable. Hereinafter, a charge transport material having a
reactive group is described by using a compound represented by
general formula (A) as an example.
##STR00002##
In general formula (A), Ar.sup.1 to Ar.sup.4 may be the same or
different and each independently represent a substituted or
unsubstituted aryl group; Ar.sup.5 represents a substituted or
unsubstituted aryl group or a substituted or unsubstituted arylene
group; D represents a side chain having a reactive group; c1 to c5
each independently represent an integer of 0 to 2; k represents 0
or 1; and the total number of D is 1 to 6.
In this exemplary embodiment, the total number of D may be 1. When
the total number of D is 2 or more, the high molecular copolymer
forms a three-dimensional crosslinked structure and the
compatibility with the reactive monomer (b) may be lowered. When a
reactive monomer with two or more D is used, the ratio of the
reactive monomer with two or more D in the copolymer may be
lowered.
In general formula (A), Ar.sup.1 to Ar.sup.4 may each be one of
compounds (1) to (7) below:
##STR00003##
In (1) to (7), R.sup.1 represents one selected from the group
consisting of a hydrogen atom, an alkyl group having 1 to 4 carbon
atoms, a phenyl group substituted with an alkyl group having 1 to 4
carbon atoms or an alkoxy group having 1 to 4 carbon atoms, an
unsubstituted phenyl group, and an aralkyl group having 7 to 10
carbon atoms; R.sup.2 to R.sup.4 each independently represent one
selected from the group consisting of a hydrogen atom, an alkyl
group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4
carbon atoms, a phenyl group substituted with an alkoxy group
having 1 to 4 carbon atoms, an unsubstituted phenyl group, an
aralkyl group having 7 to 10 carbon atoms, and a halogen atom; Ar
represents a substituted or unsubstituted arylene group; Z'
represents a divalent organic linking group; D represents a side
chain having a reactive group; c represents an integer of 0 to 2; s
represents 0 or 1; and t represents an integer of 0 to 3.
Ar in (7) may be represented by chemical formula (8) or (9)
below.
##STR00004##
In formulae (8) and (9), R.sup.5 and R.sup.6 each independently
represent one selected from the group consisting of a hydrogen
atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group
having 1 to 4 carbon atoms, a phenyl group substituted with an
alkyl group having 1 to 4 carbon atoms or an alkoxy group having 1
to 4 carbon atoms, an unsubstituted phenyl group, an aralkyl group
having 7 to 10 carbon atoms, and a halogen atom; and t' represents
an integer of 1 to 3.
In formula (7), Z' represents a divalent organic linking group and
may be one of groups represented by formulae (10) to (17)
below:
##STR00005##
In formulae (10) and (17), R.sup.7 and R.sup.8 each independently
represent one selected from the group consisting of a hydrogen
atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group
having 1 to 4 carbon atoms, a phenyl group substituted with an
alkyl group having 1 to 4 carbon atoms or an alkoxy group having 1
to 4 carbon atoms, an unsubstituted phenyl group, an aralkyl group
having 7 to 10 carbon atoms, and a halogen atom; W represents a
divalent group; q and r each independently represent an integer of
1 to 10; and t'' represents an integer of 0 to 3.
In formulae (16) and (17), W may be one of the divalent groups
represented by formulae (18) to (26) below. In formula (25), u
represents an integer of 0 to 3.
##STR00006##
In general formula (A), Ar.sup.5 represents a substituted or
unsubstituted aryl group when k is 0. Examples of the aryl group
are the same as those previously described in connection with
Ar.sup.1 to Ar.sup.4. Ar.sup.5 is a substituted or unsubstituted
arylene group when k is 1. Examples of the arylene group are those
groups obtained by removing one hydrogen atom from the previously
described examples of the aryl groups for Ar.sup.1 to Ar.sup.4.
Specific examples of the reactive monomer constituting the high
molecular copolymer (a) are described below. It should be noted
that the reactive monomer is not limited to these examples.
First, the following compounds are given as examples of the
reactive monomer having charge transport property and one reactive
group.
##STR00007## ##STR00008## ##STR00009## ##STR00010## ##STR00011##
##STR00012##
The following compounds are given as non-limiting examples of the
reactive monomer having charge transport property and two reactive
groups.
##STR00013## ##STR00014## ##STR00015## ##STR00016## ##STR00017##
##STR00018## ##STR00019## ##STR00020## ##STR00021## ##STR00022##
##STR00023## ##STR00024## ##STR00025## ##STR00026##
Next, the following compounds are given as non-limiting examples of
the reactive monomer having charge transport property and three
reactive groups.
##STR00027## ##STR00028## ##STR00029## ##STR00030## ##STR00031##
##STR00032##
The following compounds are given as non-limiting examples of the
reactive monomer having charge transport property and four reactive
groups.
##STR00033## ##STR00034## ##STR00035## ##STR00036## ##STR00037##
##STR00038## ##STR00039## ##STR00040## ##STR00041## ##STR00042##
##STR00043## ##STR00044## ##STR00045## ##STR00046## ##STR00047##
##STR00048## ##STR00049## ##STR00050## ##STR00051## ##STR00052##
##STR00053##
The reactive monomers having charge transport property described
above may also be used as the reactive monomer (b) described
below.
Compounds described in Japanese Laid-opened Patent Application
Publication Nos. 2000-206715, 2004-12986, 7-72640, 2004-302450,
2000-206717, 5-256428, 5-331238, and 9-12630, or the compounds
described above may be used as the compound having a charge
transport skeleton and an acryl or methacryl group.
The amount of the compound having the charge transport skeleton and
the acryl or methacryl group is preferably 30% to 100%, more
preferably 40% to 100%, and most preferably 50% to 100% relative to
the total solid content (mass ratio) in the coating solution. Two
or more acryl or methacryl groups may be contained in a molecule to
achieve high strength. A compound having a triphenylamine skeleton
and four or more methacryl groups in one molecule is more
preferably used. The amount of the compound having a triphenylamine
skeleton and four or more methacryl groups in one molecule is
preferably 5% or more, more preferably 10% or more, and most
preferably 15% or more relative to the total solid content (mass
ratio) in the coating solution from the viewpoint of strength.
(Reactive Monomer Having No Charge Transport Property)
In this exemplary embodiment, a (meth)acrylate monomer or oligomer
or the like having no charge transport skeleton is used as the
reactive monomer having no charge transport property, which is
another constitutional unit of the copolymer (a). In the exemplary
embodiment, "(meth)acrylate" means acrylate or methacrylate. For
example, "isobutyl(meth)acrylate" means both isobutyl acrylate and
isobutyl methacrylate.
The reactive group of the reactive monomer having no charge
transport property may be at least one, selected from the group
consisting of an acryl group, a methacryl group, a styryl group,
and derivatives thereof from the viewpoint of copolymerizability
with the reactive monomer having charge transport property.
Specific examples of the reactive monomer having no charge
transport property and constituting the copolymer (a) of this
exemplary embodiment include compounds represented by general
formula (2-1) below:
##STR00054## [In general formula (2-1), R represents an organic
group having no charge transport property, and R.sup.2 represents
hydrogen or an alkyl group having 1 to 4 carbon atoms.]
No limits are imposed as to the number of reactive groups of the
reactive monomer having no charge transport property used in this
exemplary embodiment. However, the number of reactive groups may be
1. When a reactive monomer having two or more reactive groups is
used, the ratio of the reactive monomer having two or more reactive
groups in the copolymer (a) may be low.
Examples of the reactive monomer having one reactive group include
isobutyl (meth)acrylate, t-butyl (meth)acrylate, isooctyl
(meth)acrylate, lauryl (meth)acrylate, isodecyl (meth)acrylate,
tridecyl (meth)acrylate, stearyl (meth)acrylate, isobornyl
(meth)acrylate, caprolactone (meth)acrylate, cyclohexyl
(meth)acrylate, methoxy triethylene glycol (meth)acrylate,
2-ethoxyethyl (meth)acrylate, 2-(2-ethoxyethoxy)ethyl
(meth)acrylate, tetrahydrofurfuryl(meth)acrylate, benzyl
(meth)acrylate, ethyl carbitol (meth)acrylate, phenoxyethyl
(meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl
(meth)acrylate, methoxy polyethylene glycol (meth)acrylate, methoxy
polyethylene glycol (meth)acrylate, phenoxy polyethylene glycol
(meth)acrylate, hydroxyethyl-O-phenylphenol (meth)acrylate,
O-phenylphenol glycidyl ether (meth)acrylate, alkoxylated alkyl
(meth)acrylate, and 3,3,5-trimethylcyclohexane triacrylate.
Examples of the difunctional monomer include 1,3-butylene glycol
di(meth)acrylate, 1,4-butadiene glycol di(meth)acrylate,
1,6-hexanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate,
tetraethylene glycol di(meth)acrylate, triethylene glycol
di(meth)acrylate, tripropylene glycol di(meth)acrylate, diethylene
glycol di(meth)acrylate, ethoxylated bisphenol A di(meth)acrylate,
cyclohexane dimethanol di(meth)acrylate, tricyclodecane
di(meth)acrylate, alkoxylated neopentyl glycol di(meth)acrylate,
polyethylene glycol di(meth)acrylate, and polypropylene glycol
di(meth)acrylate.
Examples of the trifunctional monomer include trimethylolpropane
tri(meth)acrylate, pentaerythritol tri(meth)acrylate, aliphatic
tri(meth)acrylate, and alkoxylated trimethylolpropane
tri(meth)acrylate. Examples of the tetrafunctional monomers include
pentaerythritol tetra(meth)acrylate, ditrimethylolpropane
tetra(meth)acrylate, and aliphatic tetra(meth)acrylate. Examples of
the penta- or higher functional monomer include dipentaerythritol
penta(meth)acrylate and dipentaerythritol hexa(meth)acrylate.
These reactive monomers having no charge transport property may be
used alone or in combination.
Among the reactive monomers having no charge transport property
described above, a reactive monomer having an ethylene oxide (EO)
group or a reactive monomer having a bisphenol skeleton is
preferred from the viewpoint of compatibility with the copolymer.
Diethylene glycol di(meth)acrylate and ethoxylated bisphenol A
di(meth)acrylate are more preferable.
From the viewpoints of mechanical strength and electrical
characteristics, the amount of the reactive monomer having no
charge transport property serving as a constitutional unit derived
from the reactive monomer in the copolymer (a) is less than 100%,
preferably 50% or less, and more preferably 30% or less in terms of
mass ratio.
The copolymer (a) of the exemplary embodiment may contain a
constitutional unit represented by general formula (1) below
derived from the reactive monomer having charge transport property
and a constitutional unit represented by general formula (2) below
derived from the reactive monomer having no charge transport
property.
##STR00055##
In general formulae (1) and (2), R represents an organic group
having no charge transport property, R.sup.1 and R.sup.2 each
independently represent hydrogen or an alkyl group having 1 to 4
carbon atoms, X represents a divalent organic group having 1 to 10
carbon atoms, a represents 0 or 1, and CT represents an organic
group having a charge transport skeleton. X may include at least
one substituent selected from the group consisting of a carbonyl
group, an ester group, an alkyl group having 1 to 4 carbon atoms,
and an aromatic ring.
In this exemplary embodiment, the copolymer (a) is obtained by
polymerizing a charge transport material having a reactive group
and a reactive monomer having no charge transport property in, for
example, a solution in the presence of a polymerization initiator.
The polymerization initiator may be a thermal polymerization
initiator or a photo polymerization initiator.
Examples of the thermal polymerization initiator include azo-based
initiators such as V-30, V-40, V-59, V-601, V-65, V-70, VE-073,
VF-096, Vam-110, and Vam-111 (products of Wako Pure Chemical
Industries), OTazo-15, OTazo-30, AIBN, AMBN, ADVN, and ACVA
(products of Otsuka Pharmaceutical Co., Ltd.), PERTETRA A, PERHEXA
HC, PERHEXA C, PERHEXA V, PERHEXA 22, PERHEXA MC, PERBUTYL H,
PERCUMYL H, PERCUMYL P, PERMENTA H, PEROCTA H, PERBUTYL C, PERBUTYL
D, PERHEXYL D, PEROYL IB, PEROYL 355, PEROYL L, PEROYL SA, NYPER
BW, NYPER BMT-K40/M, PEROYL IPP, PEROYL NPP, PEROYL TOP, PEROYL
OPP, PEROYL SBP, PERCUMYL ND, PEROCTA ND, PERHEXYL ND, PERBUTYL ND,
PERBUTYL NHP, PERHEXYL PV, PERBUTYL PV, PERHEXA 250, PEROCTA O,
PERHEXYL O, PERBUTYL O, PERBUTYL L, PERBUTYL 355, PERHEXYL I,
PERBUTYL I, PERBUTYL E, PERHEXA 25Z, PERBUTYL A, PERHEXYL Z,
PERBUTYL ZT, and PERBUTYL Z (products of NOF COPORATION), Kayaketal
AM-055, Trigonox 36-C75, Laurox, Perkadox L-W75, Perkadox CH-50L,
Trigonox TMBH, Kayacumene H, Kayabutyl H-70, Perkadox BC-FF,
Kayahexa AD, Perkadox 14, Kayabutyl C, Kayabutyl D, Kayahexa
YD-E85, Perkadox 12-XL25, Perkadox 12-EB20, Trigonox 22-N70,
Trigonox 22-70E, Trigonox D-T50, Trigonox 423-C70, Kayaester
CND-C70, Kayaester CND-W50, Trigonox 23-C70, Trigonox 23-W50N,
Trigonox 257-C70, Kayaester P-70, Kayaester TMPO-70, Trigonox 121,
Kayaester O, Kayaester HTP-65W, Kayaester AN, Trigonox 42, Trigonox
F-C50, Kayabutyl B, Kayacarbon EH-C70, Kayacarbon EH-W60,
Kayacarbon I-20, Kayacarbon BIC-75, Trigonox 117, and Kayalen 6-70
(products of Kayaku Akzo Corporation), and Luperox 610, Luperox
188, Luperox 844, Luperox 259, Luperox 10, Luperox 701, Luperox 11,
Luperox 26, Luperox 80, Luperox 7, Luperox 270, Luperox P, Luperox
546, Luperox 554, Luperox 575, Luperox TANPO, Luperox 555, Luperox
570, Luperox TAP, Luperox TBIC, Luperox TBEC, Luperox JW, Luperox
TAIC, Luperox TAEC, Luperox DC, Luperox 101, Luperox F, Luperox DI,
Luperox 130, Luperox 220, Luperox 230, Luperox 233, and Luperox 531
(products of ARKEMA YOSHITOMI, LTD).
Examples of the photo polymerization initiator include
intramolecular cleavage-type initiators and hydrogen
abstraction-type initiators. Examples of the intramolecular
cleavage-type initiators include those based on benzyl ketal,
alkylphenone, aminoalkylphenone, phosphine oxide, titanocene, and
oxime. Specific examples of the benzylketal-based initiators
include 2,2-dimethoxy-1,2-diphenylethan-1-one. Examples of the
alkylphenone-based initiators include
1-hydroxy-cyclohexyl-phenyl-ketone,
2-hydroxy-2-methyl-1-phenyl-propan-1-one,
1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propan-1-one,
2-hydroxy-1-{4-[4-(2-hydroxy-2-methyl-propionyl)-benzyl]phenyl}-2-methyl--
propan-1-one, acetophenone, and
2-phenyl-2-(p-toluenesulfonyloxy)acetophenone. Examples of the
aminoalkylphenone-based initiators include
p-dimethylaminoacetophenone, p-dimethylaminopropiophenone,
2-methyl-1-(4-methylthiophenyl)-2-morpholinopropan-1-one, and
2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1,2-(dimethylami-
no)-2-[(4-methylphenyl)methyl]-1-[4-(4-morpholinyl)phenyl]-1-butanone.
Examples of the phosphine oxide-based initiator include
2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide and
bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide. Examples of the
titanocene-based initiators include
bis(.eta.5-2,4-cyclopentadien-1-yl)-bis(2,6-difluoro-3-(1H-pyrrol-1-yl)-p-
henyl)titanium. Examples of the oxime-based initiators include
1,2-octanedione, 1-[4-(phenylthio)-, 2-(0-benzoyloxime)], and
ethanone, 1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazol-3-yl]-,
1-(0-acetyloxime).
Examples of the hydrogen abstraction-type initiators include those
based on benzophenone, thioxanthone, benzyl, and Michler's ketone.
Specific examples of the benzophenone-based initiators include
2-benzoyl benzoic acid, 2-chlorobenzophenone,
4,4'-dichlorobenzophenone, 4-benzoyl-4'-methyldiphenyl sulfide, and
p,p'-bisdiethylaminobenzophenone. Examples of the
thioxanthone-based initiators include 2,4-diethylthioxanthen-9-one,
2-chlorothioxanthone, and 2-isopropylthioxanthone. Examples of the
benzyl-based initiators include benzyl, (.+-.)-camphorquinone, and
p-anisyl.
These polymerization initiators are added in an amount of 0.2% to
10%, preferably 0.5% to 8%, and more preferably 0.7% to 5% relative
to the total amount (mass ratio) of reactive monomers during
synthesis of the copolymer.
The polymerization reactions may be carried out in a low oxygen
concentration atmosphere, such as an inert gas atmosphere, with an
oxygen concentration of 10% or less, preferably 5% or less, and
more preferably 1% or less so that the chain reactions are
performed without deactivation of the radicals generated.
The molecular weight of the copolymer (a) of the exemplary
embodiment is preferably 10000 to 500000, more preferably 10000 to
250000, and most preferably 25000 to 150000 in terms of
weight-average molecular weight.
The ratio of the reactive charge transport material in the
copolymer (a) may be 20% to 95% in terms of molar ratio from the
viewpoint of electrical characteristics.
(Reactive Monomer (b))
Next, the reactive monomer (b) is described. The reactive monomer
(b) may be a reactive monomer (a reactive monomer having charge
transport property or a reactive monomer having no charge transport
property) used in the copolymer (a) described above.
The reactive monomer (b) of the exemplary embodiment may have the
same structure as the reactive monomer having charge transport
property and constituting the copolymer (a) or a structure
different from this. However, the difference between the solubility
parameter (SP value) of the reactive monomer having no charge
transport property and constituting the copolymer (a) and the
solubility parameter (SP value) of the reactive monomer (b) having
no charge transport property is adjusted to 2
(cal/cm.sup.3).sup.1/2 or less or about 2 (cal/cm.sup.3).sup.1/2 or
less. The difference is preferably 1.6 (cal/cm.sup.3).sup.1/2 or
less and more preferably 1 (cal/cm.sup.3).sup.1/2 or less from the
viewpoints of electrical characteristics and mechanical
strength.
In this exemplary embodiment, the charge transport layer forming
the outermost surface is obtained by curing the copolymer (a) and
the reactive monomer (b). For example, the charge transport layer
may be formed by preparing a coating solution by dissolving the
copolymer (a) and the reactive monomer (b), applying the coating
solution by a blade coating technique, a wire bar coating
technique, a spray coating technique, a dip coating technique, a
bead coating technique, an air knife coating technique, a curtain
coating technique, or an ink jet technique to form a coating film,
and curing the coating film.
The outermost surface layer 3A of the exemplary embodiment is
formed by curing with light, an electron beam, or heat. In curing,
the polymerization initiator is not needed; however, in order to
obtain an outermost surface layer having high homogeneity and high
hardness, a polymerization initiator may be added. The
polymerization initiators described above may be used as the
polymerization initiator used in the exemplary embodiment. The
polymerization initiator may be a thermal polymerization initiator
and the molecular weight of the thermal polymerization initiator
may be 250 or more or about 250 or more.
The amount of the polymerization initiator added to the coating
solution is 0.2% to 10%, preferably 0.5% to 8%, and more preferably
0.7% to 5% relative to the total amount (mass ratio) of reactive
monomers.
The curing reactions may be carried out in a low oxygen
concentration atmosphere, such as an inert gas atmosphere, with an
oxygen concentration of 10% or less, preferably 5% or less, and
more preferably 1% or less so that chain reactions are performed
without deactivation of radicals generated.
The thickness of the charge transport layer 3A forming the
outermost surface is preferably 1 .mu.m to 20 .mu.m and more
preferably 3 .mu.m to 15 .mu.m, for example, in the case of the
photoconductor having the layer configuration shown in FIG. 1. The
thickness of the charge transport layer 3A is preferably 10 .mu.m
to 60 .mu.m and more preferably 20 .mu.m to 60 .mu.m, for example,
in the case of the photoconductor having the layer configuration
shown in FIG. 2.
The material contained in the charge transport layer 3A forming the
outermost surface layer of the photoconductor of the exemplary
embodiment may be contained in the charge transport layer 3B.
In this exemplary embodiment, a charge transport material having no
reactivity, a reactive material having no charge transport
property, a binder resin, etc., may be used as the materials for
the charge transport layers 3A and 3B. For example, the mechanical
strength and the charge transport property of the charge transport
layer may be effectively adjusted by selecting the type and the
amount of the charge transport substance having no reactivity
and/or the reactive material having no charge transfer
property.
First, the charge transport material having no reactive group is
described. Examples of the charge transport material having no
reactive group include electron transport compounds such as
quinone-based compounds, e.g., p-benzoquinone, chloranil, bromanil,
and anthraquinone, tetracyanoquinodimethane-based compounds,
fluorenone compounds such as 2,4,7-trinitrofluorenone,
xanthone-based compounds, benzophenone-based compounds,
cyanovinyl-based compounds, and ethylene-based compounds; and hole
transport compounds such as triarylamine-based compounds,
benzidine-based compounds, arylalkane-based compounds,
aryl-substituted ethylene-based compounds, stilbene-based
compounds, anthracene-based compounds, and hydrazone-based
compounds.
From the viewpoint of charge mobility, triarylamine derivatives
represented by structural formula (a-1) below or benzidine
derivatives represented by structural formula (a-2) below are
preferred.
##STR00056##
In formula (a-1), R.sup.9 represents a hydrogen atom or a methyl
group, 1 represents 1 or 2, and Ar.sup.6 and Ar.sup.7 each
represent a substituted or unsubstituted aryl group.
##STR00057##
In formula (a-2), R.sup.15 and R.sup.15' may be the same or
different and each represent a hydrogen atom, a halogen atom, an
alkyl group having 1 to 5 carbon atoms, or an alkoxy group having 1
to 5 carbon atoms; R.sup.16, R.sup.16', R.sup.17, and R.sup.17' may
be the same or different and each represent a hydrogen atom, a
halogen atom, an alkyl group having 1 to 5 carbon atoms, an alkoxy
group having 1 to 5 carbon atoms, an amino group substituted with
an alkyl group having 1 to 2 carbon atoms, or a substituted or
unsubstituted aryl group; and m and n each represent an integer of
0 to 2.
A polymeric charge transport material having no reactivity, such as
poly-N-vinyl carbazole and polysilane, may also be used. Among
available non-cross-linking polymeric charge transport materials,
polyester-based polymeric charge transport materials disclosed in
Japanese Laid-opened Patent Application Publication Nos. 8-176293
and 8-208820 are particularly preferable for their high charge
transport property. Although the polymeric charge transport
materials may be formed into layers alone, layers may be formed by
adding binder resins described below. The charge transport
materials are used alone or as a mixture of two or more types but
are not limited to those described above.
The materials described above may be used as the reactive material
having no charge transport property.
(Binder Resin)
Specific examples of the binder resin used in the charge transport
layer constituting the outermost surface layer include
polycarbonate resin, polyester resin, polyarylate resin, methacryl
resin, acrylic resin, polyvinyl chloride resin, polyvinylidene
chloride resin, polystyrene resin, polyvinyl acetate resin,
styrene-butadiene copolymer, vinylidene chloride-acrylonitrile
copolymer, vinyl chloride-vinyl acetate copolymer, vinyl
chloride-vinyl acetate-maleic anhydride copolymer, silicone resin,
silicone-alkyd resin, phenol-formaldehyde resin, styrene-alkyd
resin, poly-N-vinylcarbazole, and polysilane. As discussed above,
polyester-based polymeric charge transport materials such as those
disclosed in Japanese Laid-opened Patent Application Publication
Nos. 8-176293 and 8-208820 may be used as the binder resin. These
binder resins are used alone or as a mixture of two or more types.
The blend ratio of the charge transport material to the binder
resin is preferably 10:1 to 1:5 and more preferably 8:1 to 1:3 on a
mass basis.
Of these, polycarbonate resin and polyarylate resin having high
charge transport property and compatibility with the charge
transport material are preferable. When a layer containing a
compound having a triphenylamine skeleton and four or more
methacryl groups in a molecule is formed as a surface layer on the
charge transport layer, the binder resin used in the charge
transport layer preferably has a viscosity-average molecular weight
of 50000 or more and more preferably 55000 or more to improve the
adhesiveness, crack resistance during formation of the upper layer,
etc.
Examples of the techniques used to coat the charge generation layer
with a coating solution for forming a charge transfer layer include
a blade coating technique, a wire bar coating technique, a spray
coating technique, a dip coating technique, a bead coating
technique, an air knife coating technique, a curtain coating
technique, and an ink jet technique.
The total thickness of the charge transport layer is preferably 10
.mu.m to 60 .mu.m and more preferably 20 .mu.m to 60 .mu.m.
The charge transport layer of the exemplary embodiment may contain
a polymer that reacts with or does not react with a compound having
a charge transport skeleton and an acryl group or a methacryl group
to enhance discharge gas resistance, mechanical strength, scratch
resistance, particle dispersing property, viscosity control, torque
reduction, and wear control, and extend pot life.
Examples of the polymer that reacts with the compound include those
disclosed in Japanese Laid-opened Patent Application Publication
Nos. 5-216249, 5-323630, 11-52603, and 2000-264961. Examples of the
polymer that does not react with the compound include polycarbonate
resin, polyester resin, polyarylate resin, methacryl resin, acrylic
resin, polyvinyl chloride resin, polyvinylidene chloride resin, and
polystyrene resin. These polymers may be used in an amount of 100%
or less, preferably 50% or less, and more preferably 30% or less
relative to the total amount of the compound having charge transfer
property.
The charge transport layer of the exemplary embodiment may further
contain a coupling agent, a fluorine compound, etc., to control the
film-forming property, plasticity, lubricity, and adhesiveness.
Examples of the compound include various silane coupling agents and
commercially available silicone-based hard coating agents.
Examples of the silane coupling agent to be used include
vinyltrichlorosilane, vinyltrimethoxysilane, vinyltriethoxysilane,
.gamma.-glycidoxypropylmethyldiethoxysilane,
.gamma.-glycidoxypropyltrimethoxysilane,
.gamma.-glycidoxypropyltrimethoxysilane,
.gamma.-aminopropyltriethoxysilane,
.gamma.-aminopropyltrimethoxysilane,
.gamma.-aminopropylmethyldimethoxysilane,
N-.beta.(aminoethyl).gamma.-aminopropyltriethoxysilane,
tetramethoxysilane, methyltrimethoxysilane, and
dimethyldimethoxysilane. Examples of the commercially available
hard coating agents to be used include KP-85, X-40-9740, and X-8239
(products of Shin-Etsu Chemical Co., Ltd.), and AY42-440, AY42-441,
and AY49-208 (products of Dow Corning Toray Co., Ltd.). A
fluorine-containing compound may be added to impart water
repellency or the like. Examples of the fluorine-containing
compound include
(tridecafluoro-1,1,2,2-tetrahydrooctyl)triethoxysilane,
(3,3,3-trifluoropropyl)trimethoxysilane,
3-(heptafluoroisopropoxy)propyltriethoxysilane,
1H,1H,2H,2H-perfluoroalkyltriethoxysilane,
1H,1H,2H,2H-perfluorodecyltriethoxysilane, and
1H,1H,2H,2H-perfluorooctyltriethoxysilane. The amount of the silane
coupling agent to be used may be any but the amount of the
fluorine-containing compound may be of 0.25 times the amount of the
compound that does not contain fluorine or less in terms of mass.
When the amount used exceeds this, the formation of the crosslinked
layer may be adversely affected. A reactive fluorine compound such
as one disclosed in Japanese Laid-opened Patent Application
Publication 2001-166510 may be added.
The first layer and/or the second layer may contain a resin that
dissolves in alcohol to enhance discharge gas resistance,
mechanical strength, scratch resistance, particle dispersing
property, viscosity control, torque reduction, and wear control,
and extend pot life.
In preparing a coating solution by reacting the components
described above, the components may be simply mixed and dissolved
but may be heated to a temperature of room temperature (20.degree.
C.) or more and 100.degree. C. or less and preferably 30.degree. C.
or more and 80.degree. C. or less for 10 minutes to 100 hours and
preferably 1 hour to 50 hours. During preparation, ultrasonic waves
may be applied. As a result, local reactions may proceed,
homogeneity of the coating solution increases, and a film having
fewer film defects may be easily obtained.
An antioxidant may be added to the charge transport layer to
prevent deterioration caused by oxidizing gas such as ozone
generated by the charging device. When the mechanical strength of
the photoconductor is increased and the lifetime of the
photoconductor is extended, the photoconductor comes into contact
with the oxidizing gas for a longer period of time. Thus, a higher
oxidation resistance is desirable. The antioxidant is preferably a
hindered phenol-based or hindered amine-based antioxidant. An
organic sulfur-based antioxidant, a phosphite-based antioxidant, a
dithiocarbamate-based antioxidant, a thiourea-based antioxidant, a
benzimidazole-based antioxidant, or other known antioxidant may be
used as the antioxidant. The amount of the antioxidant added is
preferably 20 mass % or less and more preferably 10 mass % or
less.
Examples of the hindered phenol-based antioxidant include IRGANOX
1076, IRGANOX 1010, IRGANOX 1098, IRGANOX 245, IRGANOX 1330,
IRGANOX 3114, and IRGANOX 1076 (products of Ciba Japan KK), and
3,5-di-t-butyl-4-hydroxybiphenyl.
Examples of the hindered amine-based antioxidant include SANOL
LS2626, SANOL LS765, SANOL LS770, and SANOL LS744 (products of
Sankyo Lifetech Co., Ltd.), TINUVIN 144 and TINUVIN 622LD (products
of Ciba Japan KK), and MARK LA57, MARK LA67, MARK LA62, MARK LA68,
and MARK LA63 (products of Adeka Corporation). Examples of the
thioether-based antioxidant include Sumilizer TPS and Sumilizer
TP-D (products of Sumitomo Chemical CO., Ltd.). Examples of the
phosphite-based antioxidant include MARK 2112, MARK PEP-8, MARK
PEP-24G, MARK PEP-36, MARK 329K, and MARK HP-10 (products of Adeka
Corporation).
In order to decrease the residual potential or increase the
mechanical strength, conductive particles or organic or inorganic
particles may be added to the charge transport layer. An example of
the particles is silicon-containing particles. Silicon-containing
particles are particles containing silicon as a constitutional
element. Specific examples thereof include colloidal silica and
silicone particles. Colloidal silica used as silicon-containing
particles is selected from those prepared by dispersing silica
having an average particle size of 1 .mu.m to 100 nm and more
preferably 10 nm to 30 nm in an acidic or alkaline aqueous medium
or an organic solvent such as alcohol, ketone, or ester, and may be
a commercially available product. The solid content of the
colloidal silica in the first layer is not particularly limited but
is preferably 0.1 mass % to 50 mass % and more preferably 0.1 mass
% to 30 mass % relative to the total solid content from the
viewpoints of film-forming property, electrical characteristics,
and strength.
The silicone particles used as the silicon-containing particles are
selected from silicone resin particles, silicone rubber particles,
and silicone surface-treated silica particles. A commercially
available product is generally used as the silicone particles.
These silicone particles may be spherical with an average particle
size of 1 nm to 500 nm and preferably 10 nm to 100 nm. The silicone
particles are chemically inert and are small particles that have
good dispersibility in a resin. Since the silicone particle content
for obtaining sufficient characteristics is low, the silicone
particles improve the surface characteristics of the
electrophotographic photoconductor without obstructing crosslinking
reactions. In other words, the silicone particles evenly trapped in
a robust crosslinked structure improve the lubricity and water
repellency of the electrophotographic photoconductor surface and
offer good wear resistance and antifouling property over a long
period of time.
The silicone particle content in the outermost surface layer is
preferably 0.1 mass % to 30 mass % and more preferably 0.5 mass %
to 10 mass % relative to the total solid content.
Other examples of the particles include fluorine-based particles
such as ethylene tetrafluoride, ethylene trifluoride, propylene
hexafluoride, vinyl fluoride, and vinylidene fluoride particles,
particles composed of a copolymer resin derived from a
fluorine-based resin and a hydroxyl-containing monomer such as one
described in "8th Polymer Material Forum, Lecture abstract, p. 89",
and semiconductor metal oxides such as ZnO--Al.sub.2O.sub.3,
SnO.sub.2--Sb.sub.2O.sub.3, In.sub.2O.sub.3--SnO.sub.2,
ZnO.sub.2--TiO.sub.2, ZnO--TiO.sub.2, MgO--Al.sub.2O.sub.3,
FeO--TiO.sub.2, TiO.sub.2, SnO.sub.2, In.sub.2O.sub.3, ZnO, and
MgO.
Oil such as silicone oil may be added for the same purpose.
Examples of the oil include silicone oil such as
dimethylpolysiloxane, diphenylpolysiloxane, and
phenylmethylsiloxane; reactive silicone oil such as amino-modified
polysiloxane, epoxy-modified polysiloxane, carboxyl-modified
polysiloxane, carbinol-modified polysiloxane, methacryl-modified
polysiloxane, mercapto-modified polysiloxane, and phenol-modified
polysiloxane; cyclic dimethylcyclosiloxanes such as
hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane,
decamethylcyclopentasiloxane, and dodecamethylcyclohexasiloxane;
cyclic methylphenylcyclosiloxane such as
1,3,5-trimethyl-1,3,5-triphenylcyclotrisiloxane,
1,3,5,7-tetramethyl-1,3,5,7-tetraphenylcyclotetrasiloxane, and
1,3,5,7,9-pentamethyl-1,3,5,7,9-pentaphenylcyclopentasiloxane;
cyclic phenylcyclosiloxanes such as hexaphenylcyclotrisiloxane;
fluorine-containing cyclosiloxanes such as
3-(3,3,3-trifluoropropyl)methylcyclotrisiloxane;
hydrosilyl-containing cyclosiloxanes such as methylhydrosiloxane
mixtures, pentamethylcyclopentasiloxane, and
phenylhydrocyclosiloxane; and vinyl-containing cyclosiloxanes such
as pentavinylpentamethylcyclopentasiloxane.
A metal, metal oxide, carbon black, or the like may also be added.
Examples of the metal include aluminum, zinc, copper, chromium,
nickel, silver, and stainless steel and those metals
vapor-deposited on surfaces of plastic particles. Examples of the
metal oxide include zinc oxide, titanium oxide, tin oxide, antimony
oxide, indium oxide, bismuth oxide, tin-doped indium oxide,
antimony- or tantalum-doped tin oxide, and antimony-doped zirconium
oxide. These may be used alone or in combination. When two or more
of these materials are used in combination, the materials may
simply be mixed, or fused, or prepared as a solid solution. The
average diameter of the conductive particles is 0.3 .mu.m or less
and preferably 0.1 .mu.m or less from the viewpoint of
transparency.
<Conductive Substrate>
Examples of the conductive substrate 4 include metal plates
containing metals such as aluminum, copper, zinc, stainless steel,
chromium, nickel, molybdenum, vanadium, indium, gold, and platinum
or alloys thereof, metal drums, metal belts, and paper, plastic
films, belts, etc., on which a conductive polymer, a conductive
compound such as indium oxide, a metal such as aluminum, palladium,
or gold, or an alloy is applied, vapor-deposited, or laminated.
When the electrophotographic photoconductor is used in a laser
printer, in order to prevent interference fringe from occurring
during irradiation with laser beams, the surface of the conductive
substrate 4 may be roughened to exhibit a center line average
roughness Ra of 0.04 .mu.m to 0.5 .mu.m. When Ra is less than 0.04
.mu.m, the surface is close to a mirror surface and the
interference-preventing effect tends to be insufficient. When Ra
exceeds 0.5 .mu.m, the image quality tends to be rough even when a
coating is formed. Note that when incoherent light is used as a
light source, the surface roughening for preventing interference
fringe may be omitted. Since this prevents generation of defects
caused by irregularities in the surface of the conductive substrate
4, the lifetime may be extended.
The surface roughening may be conducted by a wet honing involving
suspending an abrasive in water and spraying the resulting
suspension onto a support, by center-less polishing involving
pressing a support against a rotating grindstone and continuously
conducting polishing, or by anodization.
Another example of a method for roughening the surface involves
dispersing conductive or semiconducting powder in a resin and
forming a layer on a surface of a support using the dispersion of
the particles so that the surface has roughness due to the
particles dispersed in the layer without roughening the conductive
substrate 4 itself.
The roughening by anodization involves forming an oxide layer on an
aluminum surface by oxidizing an aluminum anode in an electrolytic
solution. Examples of the electrolytic solution include a sulfuric
acid solution and an oxalic acid solution. However, the porous
oxide layer formed by anodization is chemically active as is, is
susceptible to contamination, and has a resistance that greatly
varies depending on the environment. Accordingly, the pores of the
anode oxide layer may be sealed by volume expansion caused by
hydration reactions using compressed water vapor or boiling water
(a metal salt such as nickel may be added) so that the anode oxide
layer turns into a more stable hydrated oxide (pore-sealing
treatment).
The thickness of the anode oxide layer may be 0.3 .mu.m to 15
.mu.m. When the thickness is less than 0.3 .mu.m, the barrier
property against injection tends to be poor and the effect tends to
be insufficient. In contrast, when the thickness exceeds 15 .mu.m,
the potential tends to increase by repeated use.
The conductive substrate 4 may be treated with an acidic aqueous
solution or a Boehmite treatment. The treatment using an acidic
treatment solution composed of phosphoric acid, chromic acid, and
hydrofluoric acid is conducted as follows. First, an acidic
treatment solution is prepared. The blend ratios of phosphoric
acid, chromic acid, and hydrofluoric acid are as follows: 10 to 11
mass % phosphoric acid, 3 to 5 mass % chromic acid, and 0.5 to 2
mass % hydrofluoric acid. The total concentration of these acids
may be in the range of 13.5 to 18 mass %. The temperature of
treatment may be 42.degree. C. to 48.degree. C. A thick film may be
formed at a higher rate when the temperature of treatment is
maintained high. The thickness of the coating film may be 0.3 .mu.m
to 15 .mu.m. When the thickness is less than 0.3 .mu.m, the barrier
property against injection tends to be poor and the effect tends to
be insufficient. In contrast, when the thickness exceeds 15 .mu.m,
the rest potential tends to increase by repeated use.
The Boehmite treatment is conducted by dipping the support in pure
water at 90.degree. C. to 100.degree. C. for 5 to 60 minutes or
bringing the support in contact with heated steam of 90.degree. C.
to 120.degree. C. for 5 to 60 minutes. The thickness of the coating
film may be 0.1 .mu.m to 5 .mu.m. The resulting film may be further
anodized by using an electrolytic solution having low film
dissolving property such as adipic acid, boric acid, borate,
phosphate, phthalate, maleate, benzoate, tartrate, or citrate.
<Undercoat Layer>
The undercoat layer 1 may be composed of a binder resin alone or a
binder resin and inorganic particles.
Inorganic particles having a powder resistance (volume resistivity)
of 10.sup.2 .OMEGA.cm to 10.sup.11.OMEGA.cm may be used as the
inorganic particles so that the undercoat layer 1 obtains an
adequate resistance for achieving leak resistance and carrier
blocking property. When the resistance value of the inorganic
particles is lower than the lower limit of this range, sufficient
leak resistance is not obtained. When the resistance value exceeds
the upper limit of this range, the rest potential may be
increased.
Among inorganic particles having the above-described resistance
value, inorganic particles of tin oxide, titanium oxide, zinc
oxide, zirconium oxide, etc., are preferred, and zinc oxide is
particularly preferable.
The inorganic particles may be subjected to a surface treatment. A
mixture of two types of inorganic particles subjected to different
surface treatments or having different particle sizes may also be
used.
Inorganic particles having a BET specific surface of 10 m.sup.2/g
or more may be used as the inorganic particles. Inorganic particles
having a BET specific surface less than 10 m.sup.2/g are likely to
cause a decrease in charging property and it is difficult to obtain
good electrophotographic characteristics.
When the inorganic particles and an acceptor compound are
contained, the long-term stability of the electrical
characteristics and the carrier blocking property are improved. The
acceptor compound may be any compound that achieves desired
characteristics but is preferably an electron transport substance
such as quinone-based compounds such as chloranil and bromanil,
tetracyanoquinodimethane-based compounds, fluorene compounds such
as 2,4,7-trinitrofluorenone and 2,4,5,7-tetranitro-9-fluorenone,
oxadiazole-based compounds such as 2-(4-biphenyl)-5-(4-t-butyl
phenyl)-1,3,4-oxadiazole, 2,5-bis(4-naphthyl)-1,3,4-oxadiazole, and
2,5-bis(4-diethylaminophenyl)-1,3,4-oxadiazole, xanthone-based
compounds, thiophene compounds, and diphenoquinone compounds such
as 3,3',5,5'-tetra-t-butyldiphenoquinone. In particular, compounds
having an anthraquinone structure are preferred. Preferred examples
of the acceptor compound having an anthraquinone structure include
hydroxyanthraquinone-based compounds, aminoanthraquinone-based
compounds, and aminohydroxyanthraquinone-based compounds. Specific
examples thereof include anthoraquinone, alizarin, quinizarin,
anthrarufin, and purpurin.
The acceptor compound content may be set to any value within the
range that achieves the desired characteristics but is preferably
0.01 mass % to 20 mass % relative to the inorganic particles. The
acceptor compound content is preferably 0.05 to 10 mass % from the
viewpoint of preventing charge accumulation and aggregation of
inorganic particles. Aggregation of inorganic particles not only
results in formation of uneven conduction paths and deterioration
of maintainability such as an increase in rest potential due to
repeated use but also tends to cause image quality defects such as
black spots.
The acceptor compound may be added at the time of forming the
undercoat layer by application or may be allowed to adhere on the
surfaces of the inorganic particles in advance. Examples of the
techniques for imparting the acceptor compound to the surfaces of
the inorganic particles include a dry technique or a wet
technique.
When the surface treatment is conducted by a dry technique, the
acceptor compound as is or dissolved in an organic solvent is added
dropwise and sprayed together with dry air or nitrogen gas toward
the inorganic particles being stirred in a mixer or the like at a
large shear force so that the treatment is homogeneously conducted.
The addition or spraying may be conducted at a temperature less
than the boiling point of the solvent. When spraying is conducted
at a temperature equal to or higher than the boiling point of the
solvent, the solvent evaporates before the particles and the
compound are homogeneously mixed, resulting in uneven distribution
of the acceptor compound and uneven treatment. Upon completion of
addition or spraying, baking may be conducted at a temperature of
100.degree. C. or higher. Baking may be conducted at any
temperature for any length of time as long as desired
electrophotographic characteristics are obtained.
According to a wet technique, homogeneous treatment is conducted as
follows. Inorganic particles are stirred in a solvent and dispersed
using ultrasonic waves, a sand mill, an attritor, a ball mill, or
the like. The acceptor compound is added to the dispersed inorganic
particles, stirred, and dispersed. Then the solvent is removed from
the mixture. The solvent is removed by filtration or distillation.
After removal of the solvent, baking is conducted at a temperature
of 100.degree. C. or higher. Baking may be conducted at any
temperature for any length of time as long as desired
electrophotographic characteristics are obtained. According to the
wet technique, moisture contained in the inorganic particles is
removed before addition of the surface treating agent. The moisture
in the inorganic particles may be removed by stirring the inorganic
particles in a solvent used for surface treatment under heating or
by boiling with a solvent.
The inorganic particles may be surface-treated before addition of
the acceptor compound. The surface-treating agent may be any known
material as long as desired characteristics are obtained. Examples
thereof include silane coupling agents, titanate-based coupling
agents, aluminum-based coupling agents, and surfactants. In
particular, silane coupling agents provide good electrophotographic
characteristics. Silane coupling agents having amino groups impart
good blocking property to the undercoat layer 1 and are thus
preferable.
Any silane coupling agent having an amino group may be used as long
as desired electrophotographic characteristics are provided.
Specific examples thereof include, but are not limited to,
.gamma.-aminopropyltriethoxysilane,
N-.beta.-(aminoethyl)-.gamma.-aminopropyltrimethoxysilane,
N-.beta.-(aminoethyl)-.gamma.-aminopropylmethylmethoxysilane, and
N,N-bis(.beta.-hydroxyethyl)-.gamma.-aminopropyltriethoxysilane.
Two or more silane coupling agents may be used as a mixture.
Examples of the silane coupling agent used together with a silane
coupling agent having an amino group include, but are not limited
to, vinyltrimethoxysilane,
.gamma.-methacryloxypropyl-tris(.beta.-methoxyethoxy)silane,
.beta.-(3,4-epoxycyclohexyl)ethyltrimethoxysilane,
.gamma.-glycidoxypropyltrimethoxysilane, vinyltriacetoxysilane,
.gamma.-mercaptopropyltrimethoxysilane,
.gamma.-aminopropyltriethoxysilane,
N-.beta.-(aminoethyl)-.gamma.-aminopropyltrimethoxysilane,
N-.beta.-(aminoethyl)-.gamma.-aminopropylmethylmethoxysilane,
N,N-bis(.beta.-hydroxyethyl)-.gamma.-aminopropyltriethoxysilane,
and .gamma.-chloropropyltrimethoxysilane.
Any known surface-treating method may be used. For example, a wet
method or a dry method may be used. The addition of the acceptor
and the surface-treatment with a coupling agent and the like may be
conducted simultaneously.
The amount of the silane coupling agent relative to the inorganic
particles in the undercoat layer 1 may be set to any amount as long
as the desired electrophotographic characteristics are obtained.
However, the amount of silane coupling agent may be 0.5 to 10 mass
% relative to the inorganic particles from the viewpoint of
improving the dispersibility.
The binder resin contained in the undercoat layer 1 may be any
binder resin that forms a satisfactory film and achieves desired
characteristics. Examples thereof include polymer resins such as
acetals, e.g., polyvinyl butyral, polyvinyl alcohol resin, casein,
polyamide resin, cellulose resin, gelatin, polyurethane resin,
polyester resin, methacryl resin, acrylic resin, polyvinyl chloride
resin, polyvinyl acetate resin, vinyl chloride-vinyl acetate-maleic
anhydride resin, silicone resin, silicone-alkyd resin, phenol
resin, phenol-formaldehyde resin, melamine resin, and urethane
resin, and other known materials such as zirconium chelate
compounds, titanium chelate compounds, aluminum chelate compounds,
titanium alkoxide compounds, organic titanium compounds, and silane
coupling agents. Charge transport resins having charge transport
groups and conductive resins such as polyaniline are also used.
Among these, resins insoluble in a coating solvent of the upper
layer are preferable and phenol resins, phenol-formaldehyde resins,
melamine resins, urethane resins, epoxy resins, etc., are more
preferable. When two or more of these materials are used in
combination, the mixing ratio is set according to need.
The ratio of the metal oxide imparted with the acceptor property to
the binder resin or the ratio of the inorganic particles to the
binder resin in the coating solution for forming the undercoat
layer are freely set within the ranges that achieve desired
electrophotographic photoconductor characteristics.
Various additives for improving electrical characteristics,
environmental stability, and image quality may be used in the
undercoat layer 1. Additives may be any known materials such as
polycyclic-based and azo-based electron transport pigments,
zirconium chelate compounds, titanium chelate compounds, aluminum
chelate compounds, titanium alkoxide compounds, organic titanium
compounds, and silane coupling agents. While a silane coupling
agent is used in surface treatment of the metal oxide, it is also
added as an additive to the coating solution. Specific examples of
the silane coupling agents used here include vinyltrimethoxysilane,
.gamma.-methacryloxypropyl-tris(.beta.-methoxyethoxy)silane,
.beta.-(3,4-epoxycyclohexyl)ethyltrimethoxysilane,
.gamma.-glycidoxypropyltrimethoxysilane, vinyltriacetoxysilane,
.gamma.-mercaptopropyltrimethoxysilane,
.gamma.-aminopropyltriethoxysilane,
N-.beta.-(aminoethyl)-.gamma.-aminopropyltrimethoxysilane,
N-.beta.-(aminoethyl)-.gamma.-aminopropylmethylmethoxysilane,
N,N-bis(.beta.-hydroxyethyl)-.gamma.-aminopropyltriethoxysilane,
and .gamma.-chloropropyltrimethoxysilane. Examples of the zirconium
chelate compounds include zirconium butoxide, zirconium ethyl
acetoacetate, zirconium triethanolamine, acetylacetonate zirconium
butoxide, ethyl acetoacetonate zirconium butoxide, zirconium
acetate, zirconium oxalate, zirconium lactate, zirconium
phosphonate, zirconium octanate, zirconium naphthenate, zirconium
laurate, zirconium stearate, zirconium isostearate, methacrylate
zirconium butoxide, stearate zirconium butoxide, and isostearate
zirconium butoxide.
Examples of the titanium chelate compounds include tetraisopropyl
titanate, tetra-n-butyl titanate, butyl titanate dimer,
tetra(2-ethyl hexyl)titanate, titanium acetylacetonate,
polytitanium acetylacetonate, titanium octylene glycolate, titanium
lactate ammonium salt, titanium lactate, titanium lactate ethyl
ester, titanium triethanol aminate, and polyhydroxytitanium
stearate.
Examples of the aluminum chelate compounds include aluminum
isopropylate, monobutoxy aluminum diisopropylate, aluminum
butyrate, diethyl acetoacetate aluminum diisopropylate, and
aluminum tris(ethyl acetoacetate).
These compounds may be used alone or as a mixture or a
polycondensate of two or more.
The solvent for preparing the coating solution for forming the
undercoat layer is selected from known organic solvents, e.g.,
alcohol-based, aromatic-based, halogenated hydrocarbon-based,
ketone-based, ketone alcohol-based, ether-based, and ester-based
organic solvents. Examples of the organic solvent include methanol,
ethanol, n-propanol, iso-propanol, n-butanol, benzylalcohol, methyl
cellosolve, ethyl cellosolve, acetone, methyl ethyl ketone,
cyclohexanone, methyl acetate, ethyl acetate, n-butyl acetate,
dioxane, tetrahydrofuran, methylene chloride, chloroform,
chlorobenzene, and toluene.
The solvent used for dispersing these may be one solvent or a
mixture of two or more solvents. When a mixture is used, the
solvent used may be any solvent that dissolves a binder resin as a
mixed solvent.
Examples of the devices used for dispersion include roll mills,
ball mills, vibrating ball mills, attritors, sand mills, colloid
mills, and paint shakers. Examples of the coating technique used
for forming the undercoat layer 1 include common techniques such as
a blade coating technique, a wire bar coating technique, a spray
coating technique, a dip coating technique, a bead coating
technique, an air knife coating technique, and a curtain coating
technique.
The undercoat layer 1 is formed on the conductive substrate by
using the coating solution for forming the undercoating layer
obtained as such.
The Vickers hardness of the undercoat layer 1 may be 35 or
more.
The thickness of the undercoat layer 1 may be any as long as
desired characteristics are achieved. For example, the thickness
may be 15 .mu.m or more and preferably 15 to 50 .mu.m.
When the thickness of the undercoat layer 1 is less than 15 .mu.m,
sufficient anti-leakage property is not obtained. When the
thickness exceeds 50 .mu.m, the rest potential tends to remain
during long use and abnormality in image density is likely to
occur.
The surface roughness (ten-point average roughness) of the
undercoat layer 1 is adjusted to 1/4n (n is a refractive index of
the upper layer) of the exposure laser wavelength .lamda. to
1/2.lamda. to prevent moire patterns. Particles such as resin
particles may be added to the undercoat layer to adjust the surface
roughness. Examples of the resin particles include silicone resin
particles and crosslinked PMMA resin particles.
The undercoat layer may be polished to adjust the surface
roughness. Examples of the polishing technique include buff
polishing, sand blasting, wet horning, and grinding.
The applied coating solution is dried to obtain an undercoat layer.
Typically, drying is conducted at a temperature at which the
solvent is evaporated and a film is formed.
<Charge Generation Layer>
The charge generation layer 2 is a layer that contains a charge
generation material and a binder resin.
Examples of the charge generation material include azo pigments
such as bisazo and trisazo; polycyclic aromatic pigments such as
dibromoanthanthrone, perylene pigments, pyrrolopyrrole pigments,
phthalocyanine pigments, zinc oxide, and trigonal selenium. Of
these, metal or non-metal phthalocyanine pigments are preferred for
the exposure to near infrared. In particular, hydroxygallium
phthalocyanine disclosed in, for example, Japanese Laid-opened
Patent Application Publication Nos. 5-263007 and 5-279591,
chlorogallium phthalocyanine disclosed in, for example, Japanese
Laid-opened Patent Application Publication No. 5-98181, dichlorotin
phthalocyanine disclosed in, for example, Japanese Laid-opened
Patent Application Publication Nos. 5-11172 and 5-11173, and
titanyl phthalocyanine disclosed in Japanese Laid-opened Patent
Application Publication Nos. 4-189873 and 5-43823 are more
preferable. For the exposure to near ultraviolet laser beams,
polycyclic aromatic pigments such as dibromoanthanthrone,
thioindigo-based pigments, porphyrazine compounds, zinc oxide,
trigonal selenium, and bisazo pigments described in Japanese
Laid-opened Patent Application Publication Nos. 2004-78147 and
2005-181992 are more preferable.
The binder resin used in the charge generation layer 2 is selected
from a wide range of insulating resins. The binder resin may be
selected from organic photoconductive polymer such as
poly-N-vinylcarbazole, polyvinylanthracene, polyvinylpyrene, and
polysilane. Examples of the binder resin include polyvinylbutyral
resin, polyarylate resin (polycondensate of a bisphenol and an
aromatic divalent carboxylic acid, etc.), polycarbonate resin,
polyester resin, phenoxy resin, vinyl chloride-vinyl acetate
copolymer, polyamide resin, acrylic resin, polyacrylamide resin,
polyvinylpyridine resin, cellulose resin, urethane resin, epoxy
resin, casein, polyvinyl alcohol resin, and polyvinyl pyrrolidone
resin. These binder resins are used alone or as a mixture of two or
more types. The blend ratio of the charge generation material to
the binder resin may be in the range of 10:1 to 1:10 in terms of
mass ratio.
The charge generation layer 2 is formed by using a coating solution
prepared by dispersing the charge generation material and a binder
resin in a solvent.
Examples of the solvent used for dispersion include methanol,
ethanol, n-propanol, n-butanol, benzylalcohol, methyl cellosolve,
ethyl cellosolve, acetone, methyl ethyl ketone, cyclohexanone,
methyl acetate, n-butyl acetate, dioxane, tetrahydrofuran,
methylene chloride, chloroform, chlorobenzene, and toluene. These
may be used alone or as a mixture of two or more types.
The technique for dispersing the charge generation material and the
binder resin in a solvent include common techniques such as a ball
mill dispersion technique, an attritor dispersion technique, and a
sand mill dispersion technique. The change in crystal type of the
charge generation material caused by dispersion is suppressed when
such a dispersion technique is used. For the dispersion, it is
effective to adjust the average particle size of the charge
generation material to 0.5 .mu.m or less, preferably 0.3 .mu.m or
less, and more preferably 0.15 .mu.m or less.
A common technique is used to form the charge generation layer 2.
Examples of the technique include a blade coating technique, a wire
bar coating technique, a spray coating technique, a dip coating
technique, a bead coating technique, an air knife coating
technique, and a curtain coating technique.
The thickness of the charge generation layer 2 obtained as such is
preferably 0.1 .mu.m to 5.0 .mu.m and more preferably 0.2 .mu.m to
2.0 .mu.m.
<Method for Preparing Electrophotographic Photoconductor>
A method for preparing the electrophotographic photoconductor of
this exemplary embodiment includes a step of sequentially forming,
if needed, an undercoat layer 1, a charge generation layer 2, and a
charge transport layer 3B on a conductive substrate 4 and then
forming an outermost surface layer by applying a coating solution
containing a copolymer (a) derived from a reactive monomer having
charge transport property and a reactive monomer having no charge
transport property, and a reactive monomer (b) that has a
solubility parameter (SP value) different from the solubility
parameter (SP value) of the reactive monomer having no charge
transport property, i.e., a constitutional unit of the copolymer
(a), by 2 (cal/cm.sup.3).sup.1/2 or less or about 2
(cal/cm.sup.3).sup.1/2 or less; and a step of heating the coating
film of the coating solution at an oxygen concentration of 1000 ppm
or less or about 1000 ppm or less and a temperature of 130.degree.
C. or higher or about 130.degree. C. or higher. From the viewpoint
of mechanical strength, the oxygen concentration in the heating
step may be 200 ppm or less. From the viewpoints of mechanical
strength and electrical characteristics, the heating temperature
may be 130.degree. C. to 175.degree. C.
When the heating step is conducted under the aforementioned
conditions, a charge transport layer 3A having good mechanical
strength and electrical characteristics is formed.
<Process Cartridge and Image Forming Apparatus>
Next, a process cartridge and an image forming apparatus that use
the electrophotographic photoconductor of the exemplary embodiment
are described.
The process cartridge of the exemplary embodiment includes the
electrophotographic photoconductor of the aforementioned exemplary
embodiment. The process cartridge is detachably attachable to an
image forming apparatus that forms an image on a recording medium
by transferring a toner image, which has been obtained by
developing an electrostatic latent image on a surface of the
photoconductor, onto the recording medium.
The image forming apparatus of the exemplary embodiment includes
the electrophotographic photoconductor of the aforementioned
exemplary embodiment, a charging device that charges the
electrophotographic photoconductor, a latent image forming device
that forms an electrostatic latent image on a surface of the
charged electrophotographic photoconductor, a developing device
that forms a toner image by developing the electrostatic latent
image on the surface of the electrophotographic photoconductor with
a toner, and a transfer device that transfers the toner image
formed on the surface of the electrophotographic photoconductor
onto a recording medium. The image forming apparatus of the
exemplary embodiment may be a tandem machine that includes two or
more photoconductors corresponding to toners of different colors.
In such a case, each photoconductor may be the electrophotographic
photoconductor of the exemplary embodiment. The transfer of the
toner image may be conducted by using an intermediate transfer body
(intermediate transfer system).
FIG. 3 is a schematic diagram showing an example of an image
forming apparatus (with a process cartridge) of the exemplary
embodiment. Referring to FIG. 3, an image forming apparatus 100
includes a process cartridge 300 having an electrophotographic
photoconductor 7, an exposure device 9, a transfer device 40, and
an intermediate transfer body 50. The exposure device 9 is located
at a position that that makes expose the electrophotographic
photoconductor 7 possible through an opening in the process
cartridge 300. The transfer device 40 is located at a position that
faces the electrophotographic photoconductor 7 through the
intermediate transfer body 50. The intermediate transfer body 50 is
partly in contact with the electrophotographic photoconductor
7.
The process cartridge 300 in FIG. 3 has a housing that supports the
electrophotographic photoconductor 7, a charging device 8, a
developing device 11, and a cleaning device 13. The cleaning device
13 has a cleaning blade (cleaning member) 131 positioned to contact
the surface of the electrophotographic photoconductor 7.
Although the drawing shows an example in which a fibrous member 132
(roll-shaped) that supplies a lubricant 14 onto the surface of the
photoconductor 7 and a fibrous member 133 (flat brush) that assists
cleaning are provided, these components may be omitted if not
needed.
Examples of the charging device 8 include contact-type chargers
such as a conductive or semiconductive charge roller, a charge
brush, a charge film, a charge rubber blade, and a charge tube.
Other known chargers such as non-contact-type roller chargers,
scorotron and corotron chargers that utilize corona discharge,
etc., may be used.
Although not shown in the drawing, a photoconductor heating member
for raising the temperature of the electrophotographic
photoconductor 7 and reducing the relative temperature may be
provided in the vicinity of the electrophotographic photoconductor
7.
Examples of the exposure device 9 include optical devices that
expose the surface of the photoconductor 7 to form an image with
light such as semiconductor laser light, LED light, liquid crystal
shutter light, etc. The wavelength of the light source used is in
the spectral sensitivity range of the photoconductor. The
mainstream of the wavelength of the semiconductor lasers is near
infrared that has an oscillation wavelength near 780 nm. However,
the wavelength is not limited to this. For example, lasers having
oscillation wavelengths on the order of 600 nm and lasers having
oscillation wavelengths near the range of 400 nm to 450 nm may also
be used. Moreover, in order to form color images, surface-emission
laser light sources that output multibeam are also effective.
The developing device 11 may be a common developing device that
develops images using a magnetic or non-magnetic one-component
developer or two-component developer or the like in a contact
manner or a non-contact manner. No limitation is imposed on the
developing device as long as the aforementioned functions are
achieved and a developing device is selected according to the
purpose. An example of the developing device is a developer that
causes a one-component developer or a two-component developer to
adhere on the photoconductor 7 using a brush, a roller, and the
like. In particular, a developing device that uses a developing
roller having a surface supporting a developer may be used.
The toner used in the developing device 11 is described below.
The toner used in the image forming apparatus of the exemplary
embodiment preferably has an average shape factor
((ML.sup.2/A).times.(.pi.r/4).times.100, where ML representing the
maximum length of a particle and A represents the projected area of
the particle) of 100 to 150, more preferably 105 to 145, and most
preferably 110 to 140. The toner preferably has a volume-average
particle size of 3 to 12 .mu.m and more preferably 3.5 to 9
.mu.m.
The method of making the toner is not particularly limited.
Examples of the method of making the toner includes a kneading and
pulverizing method involving kneading a binder resin, a coloring
agent, a releasing agent, a charge controlling agent, etc., and
pulverizing and classifying the kneaded mixture; a method of
changing the shape of particles prepared by a kneading and
pulverizing method by applying mechanical impact or thermal energy;
an emulsion polymerization/aggregation method involving emulsifying
a polymerizable monomer of a binder resin, mixing the dispersion
with dispersions of a coloring agent, a releasing agent, a charge
controlling agent, etc., and aggregating and thermally coalescing
the mixture to obtain toner particles; a suspension polymerization
method involving suspending solutions of a polymerizable monomer
for obtaining a binder resin, a coloring agent, a releasing agent,
a charge controlling agent, etc., in an aqueous solvent to conduct
polymerization; and a solution suspension method involving forming
particles by suspending solutions of a binder resin, a coloring
agent, a releasing agent, a charge controlling agent, etc., in an
aqueous solvent.
Another example of the method for forming the toner includes
causing aggregated particles to adhere on the toner particles
obtained by any of the methods described above, and heating and
coalescing the particles so that the particles have a core-shell
structure. The toner is preferably made by a suspension
polymerization method, an emulsion polymerization/aggregation
method, or a solution suspension method that uses an aqueous
solvent and more preferably by an emulsion
polymerization/aggregation method from the viewpoints of
controlling the shape and the particle size distribution.
Toner mother particles may contain a binder resin, a coloring
agent, and a releasing agent and may further contain silica and a
charge controlling agent.
Examples of the binder resin used in the toner mother particles
include homopolymers and copolymers of styrenes such as styrene and
chlorostyrene, monoolefins such as ethylene, propylene, butylene,
and isoprene, vinyl esters such as vinyl acetate, vinyl propionate,
vinyl benzoate, and vinyl butyrate, .alpha.-methylene aliphatic
monocarboxylic acid esters such as methyl acrylate, ethyl acrylate,
butyl acrylate, dodecyl acrylate, octyl acrylate, phenyl acrylate,
methyl methacrylate, ethyl methacrylate, butyl methacrylate, and
dodecyl methacrylate, vinyl ethers such as vinyl methyl ether,
vinyl ethyl ether, and vinyl butyl ether, vinyl ketones such as
vinyl methyl ketone, vinyl hexyl ketone, and vinyl isopropenyl
ketone, and polyester resins obtained by copolymerizing
dicarboxylic acids and diols.
Representative examples of the binder resin include polystyrene,
styrene-alkyl acrylate copolymer, styrene-alkyl methacrylate
copolymer, styrene-acrylonitrile copolymer, styrene-butadiene
copolymer, styrene-maleic anhydride copolymer, polyethylene,
polypropylene, polyester resin, polyurethane, epoxy resin, silicone
resin, polyamide, modified rosin, and paraffin wax.
Representative examples of the coloring agent include magnetic
powder such as magnetite and ferrite, carbon black, aniline blue,
Calco Oil blue, chrome yellow, ultramarine blue, Du Pont oil red,
quinoline yellow, methylene blue chloride, phthalocyanine blue,
malachite green oxalate, lamp black, rose bengal, C. I. Pigment Red
48:1, C. I. Pigment Red 122, C.I. Pigment Red 57:1, C.I. Pigment
Yellow 97, C. I. Pigment Yellow 17, C. I. Pigment Blue 15:1, and C.
I. Pigment Blue 15:3.
Representative examples of the releasing agent include low
molecular polyethylene, low molecular polypropylene,
Fischer-Tropsch wax, montan wax, carnauba wax, rice wax, and
candelilla wax.
A known charge controlling agent is used as the charge controlling
agent. For example, an azo-based metal complex compound, a metal
complex compound of salicylic acid, or a resin-type charge
controlling agent that contains a polar group is used. When the
toner is made by a wet method, raw materials that do not readily
dissolve in water may be used. The toner may be a magnetic toner
that contains a magnetic material or a non-magnetic toner that does
not contain a magnetic material.
The toner used in the developing device 11 is made by mixing the
toner mother particles described above and the external additives
with a Henschel mixer, a V blender, or the like. When the toner
mother particles are prepared by a wet method, external additives
may be added by a wet method.
Lubricating particles may be added to the toner mother particles
used in the developing device 11. Examples of the lubricating
particles include solid lubricants such as graphite, molybdenum
disulfide, talc, fatty acids, and fatty acid metal salts; low
molecular polyolefins such as polypropylene, polyethylene, and
polybutene; silicones having a softening points by heating;
aliphatic amides such as amide oleate, amide erucate, amide
ricinoleate, and amide stearate; vegetable wax such as carnauba
wax, rice wax, candelilla wax, Japan wax, and jojoba oil; animal
wax such as beeswax; mineral and petroleum wax such as montan wax,
ozokerite, ceresine, paraffin wax, microcrystalline wax, and
Fischer-Tropsch wax; and modified products of the foregoing. These
may be used alone or in combination. The average particle size may
be in the range of 0.1 .mu.m to 10 .mu.m. The particles having the
chemical structure above may be ground to make the diameter
uniform. The amount of the lubricating particles added to the toner
is preferably 0.05 mass % to 2.0 mass % and more preferably 0.1
mass % to 1.5 mass %.
Inorganic particles, organic particles, composite particles
including organic particles and inorganic particles adhered on the
organic particles may be added to the toner mother particles used
in the developing device 11.
Examples of the inorganic particles include various inorganic
oxides, nitrides, and borides such as silica, alumina, titania,
zirconia, barium titanate, aluminum titanate, strontium titanate,
magnesium titanate, zinc oxide, chromium oxide, cerium oxide,
antimony oxide, tungsten oxide, tin oxide, tellurium oxide,
manganese oxide, boron oxide, silicon carbide, boron carbide,
titanium carbide, silicon nitride, titanium nitride, and boron
nitride.
The inorganic particles may be treated with a titanium coupling
agent such as tetrabutyl titanate, tetraoctyl titanate,
isopropyltriisostearoyl titanate, isopropyltridecylbenzenesulfonyl
titanate, and bis(dioctylpyrophosphate)oxyacetate titanate, a
silane coupling agent such as
.gamma.-(2-aminoethyl)aminopropyltrimethoxysilane,
.gamma.-(2-aminoethyl)aminopropylmethyldimethoxysilane,
.gamma.-methacryloxypropyltrimethoxysilane,
N-.beta.-(N-vinylbenzylaminoethyl).gamma.-aminopropyltrimethoxysilane
hydrochloride, hexamethyldisilazane, methyltrimethoxysilane,
butyltrimethoxysilane, isobutyltrimethoxysilane,
hexyltrimethoxysilane, octyltrimethoxysilane,
decyltrimethoxysilane, dodecyltrimethoxysilane,
phenyltrimethoxysilane, o-methylphenyltrimethoxysilane, and
p-methylphenyltrimethoxysilane. The inorganic particles
hydrophobized with a higher fatty acid metal salt such as silicone
oil, aluminum stearate, zinc stearate, or calcium sterate may also
be used.
Examples of the organic particles include styrene resin particles,
styrene acrylic resin particles, polyester resin particles, and
urethane resin particles.
Organic particles that have a number-average particle size of 5 nm
to 1000 nm, preferably 5 nm to 800 nm, and more preferably 5 nm to
700 nm are used. The sum of the amounts of the aforementioned
particles and lubricating particles may be 0.6 mass % or more.
A small-diameter inorganic oxide having a primary particle size of
40 nm or less may be used as the inorganic oxide added to the toner
mother particles, and an inorganic oxide having a larger diameter
may be further added. The inorganic oxide particles may be known
particles. Silica and titanium oxide may be used in
combination.
The small-diameter inorganic oxide may be surface-treated. A
carbonate such as calcium carbonate and magnesium carbonate or an
inorganic mineral such as hydrotalcite may also be added.
The electrophotographic color toner is mixed with a carrier and
used. Examples of the carrier include iron powder, glass beads,
ferrite powder, and nickel powder coated or uncoated with a resin.
The mixing ratio of the carrier is set according to need.
Examples of the transfer device 40 include contact-type transfer
chargers that use belts, rollers, films, and rubber blades, and
scorotron transfer chargers and corotron transfer chargers that use
corona discharge.
Examples of the intermediate transfer body 50 include a belt
(intermediate transfer belt) composed of polyimide, polyamideimide,
polycarbonate, polyarylate, polyester, rubber, or the like that has
been rendered a semiconductive property. The intermediate transfer
body 50 may be a drum instead of a belt.
The image forming apparatus 100 may include an optical charge
eraser that optically erase the charges of the photoconductor 7 in
addition to the respective devices described above.
FIG. 4 is a schematic diagram showing an example of an image
forming apparatus according to another exemplary embodiment. An
image forming apparatus 120 is a full color image forming apparatus
of a tandem type equipped with four process cartridges 300 as shown
in FIG. 4. The image forming apparatus 120 includes four process
cartridges 300 aligned side by side on the intermediate transfer
body 50. One electrophotographic photoconductor is used per color.
The image forming apparatus 120 has the same structure as the image
forming apparatus 100 except for that it has a tandem system.
When the electrophotographic photoconductor of the exemplary
embodiment is used in a tandem image forming apparatus, the
electrical characteristics of the four photoconductors become
stable. Thus, quality images with good color balance are obtained
for a long time.
According to the image forming apparatus and the process cartridge
of the exemplary embodiment, the developing device may include a
developing roller which serves as a developer support that moves in
a direction opposite to the moving direction (rotation direction)
of the electrophotographic photoconductor. The developing roller
has a cylindrical developing sleeve that supports a developer at
its surface. The developing device may be equipped with a limiting
member for limiting the amount of the developer supplied to the
developing sleeve. When the developing roller is moved (rotated) in
a direction opposite to the rotation direction of the
electrophotographic photoconductor, the surface of the
electrophotographic photoconductor is rubbed with the toner
remaining between the developing roller and the electrophotographic
photoconductor.
According to the image forming apparatus of the exemplary
embodiment, the gap between the developing sleeve and the
photoconductor is preferably 200 .mu.m to 600 .mu.m and more
preferably 300 .mu.m to 500 .mu.m. The gap between the developing
sleeve and the limiting member for limiting the amount of the
developer is preferably 300 .mu.m to 1000 .mu.m and more preferably
400 .mu.m to 750 .mu.m.
The absolute value of the moving rate of the surface of the
developing roller is preferably 1.5 to 2.5 times and more
preferably 1.7 to 2.0 times the absolute value (process speed) of
the moving rate of the surface of the photoconductor.
According to the image forming apparatus (process cartridge) of the
exemplary embodiment, the developing device may be equipped with a
developer supporting member having a magnetic body and configured
to develop an electrostatic latent image with a two-component
developer containing a magnetic carrier and a toner.
As described heretofore, according to the exemplary embodiment,
stable images are obtained despite the repeated use without being
affected by the environment since the electrophotographic
photoconductor described above is used. The electrophotographic
photoconductor of the exemplary embodiment has good mechanical
strength and exhibits stable electrical characteristics over a long
time.
EXAMPLES
The present invention will now be described by using Examples below
which do not limit the scope of the present invention. Hereinafter,
"parts" refer to parts by mass unless otherwise noted.
Synthetic Example 1
Synthesis of Compound I-14
##STR00058##
Into a 1000 ml flask, 100 g of a compound (1), 107 g of methacrylic
acid, 300 ml of toluene, and 2 g of p-toluene sulfonic acid are
added and the mixture is refluxed under heating for 10 hours. Upon
completion of reaction, the mixture is cooled and put into 2000 ml
of water to be washed, and is further washed with water. The
toluene layer is dried over anhydrous sodium sulfate and purified
by silica gel column chromatography to obtain 35 g of a compound
(I-14). The IR spectrum of the compound (I-14) is shown in FIG.
6.
Synthetic Example 2
Synthesis of Copolymer
##STR00059##
Into a 500 ml flask, 20 g of compound (I-14), 5 g of
2-(2-ethoxyethoxy)ethyl acrylate, 150 g of toluene, and 0.5 g of
polymerization initiator (V601) are added. After the flask is
purged with nitrogen, the mixture is refluxed for 3 hours at
90.degree. C. under heating. The mixture is cooled to room
temperature, and 25 ml of tetrahydrofuran is added to the mixture.
The resulting solution is added to 1000 ml of methanol dropwise to
obtain a solid component. Reprecipitation is conducted twice. As a
result, 20 g of compound (2) is obtained.
Example 1
Formation of Undercoat Layer
One hundred parts of zinc oxide (average particle size: 70 nm,
product of Tayca Corporation, specific surface: 15 m.sup.2/g) and
500 parts of toluene are mixed and stirred. To the resulting
solution, 1.3 parts of a silane coupling agent KBM503, product of
Shin-Etsu Chemical. Co., Ltd.) is added, and the mixture is stirred
for 2 hours. Then toluene is removed by evaporation under a reduced
pressure and baking is conducted at 120.degree. C. for 3 hours to
obtain zinc oxide surface-treated with the silane coupling
agent.
The zinc oxide surface-treated with the silane coupling agent (110
parts) and 500 parts of tetrahydrofuran are mixed and stirred. To
the resulting mixture, a solution of 0.6 parts of alizarin in 50
parts of tetrahydrofuran is added, and the mixture is stirred at
50.degree. C. for 5 hours. The zinc oxide clad with alizarin is
separated by filtering under a reduced pressure and dried under a
reduced pressure at 60.degree. C. to obtain alizarin-clad zinc
oxide.
Thirty eight parts of a solution prepared by dispersing 60 parts of
alizarin-clad zinc oxide, 13.5 parts of curing agent (block
isocyanate, Sumidur 3175, product of Sumika Bayer Urethane Co.,
Ltd.), and 15 parts of butyral resin (S-LEC BM-1, product of
Sekisui Chemical Co., Ltd.) in 85 parts of methyl ethyl ketone is
mixed with 25 parts of methyl ethyl ketone. The mixture is
dispersed in a sand mill using glass beads having a diameter of 1
mm for 2 hours.
To the dispersion, 0.005 parts of dioctyltin dilaurate and 40 parts
of silicone resin particles (Tospearl 145, product of GE Toshiba
Silicones Co., Ltd.) are added to obtain a coating solution for
forming the undercoat layer. The coating solution for forming an
undercoat layer is applied on an aluminum substrate having a
diameter of 30 mm, a length of 340 mm, and a thickness of 1 mm by
dip-coating, and the applied solution is dried and cured at
170.degree. C. for 40 minutes to obtain an undercoat layer having a
thickness of 18 .mu.m.
(Formation of Charge Generation Layer 2)
A mixture of 15 parts of hydroxygallium phthalocyanine (charge
generation material) and at least having diffraction peaks at Bragg
angles (2.theta..+-.0.2.degree.) of 7.3.degree., 16.0.degree.,
24.9.degree., 28.0.degree. in an X-ray diffraction spectrum
observed using a Cuk.alpha. X ray, 10 parts of vinyl chloride-vinyl
acetate copolymer resin (binder resin) (VMCH, product of Nipon
Unicar Co., Ltd.), and 200 parts of n-butyl acetate is dispersed in
a sand mill for 4 hours using glass beads having a diameter of 1
mm. To the dispersion, 175 parts of n-butyl acetate and 180 parts
of methyl ethyl ketone are added. The resulting mixture is stirred
to obtain a coating solution for forming a charge generation layer.
The coating solution for forming the charge generation layer is
applied on the undercoat layer by dip coating and dried at normal
temperature (23.degree. C.) to form a charge generation layer
having a thickness of 0.2 .mu.m.
(Formation of Charge Transport Layer 3B)
A coating solution is prepared by dissolving 3.5 parts by mass of
N,N'-diphenyl-N,N'-bis(3-methylphenyl)-[1,1']biphenyl-4,4'-diamine,
1.5 parts by mass of N,N'-bis(3,4-dimethylphenyl)-biphenyl-4-amine,
and 5.0 parts by mass of bisphenol Z polycarbonate resin
(viscosity-average molecular weight: about 40,000) in 40 parts by
mass of chlorobenzene. The coating solution is applied on the
charge generation layer by dip coating and dried at 130.degree. C.
for 45 minutes. The thickness of the charge transport layer 3B is
about 20 .mu.m.
(Formation of Charge Transport Layer 3A)
A coating solution is prepared by mixing 16 parts by mass of
compound (2) prepared in the previous synthetic example, 4 parts by
mass of 2-(2-ethoxyethoxy)ethyl acrylate, 0.08 parts by weight of
polymerization initiator (OT-azo15 (product of Otsuka Chemical Co.,
Ltd.)), 30 parts by mass of cyclopentanone, 40 parts by mass of
cyclopentylmethyl ether, 30 parts by mass of toluene, 1 part by
mass of 3,5-di-t-butyl-4-hydroxytoluene (BHT), and 0.5 parts by
mass of fluorine-containing acryl polymer (KL-600, product of
KYOEISHA CHEMICAL Co., Ltd.). The coating solution is applied on
the charge transport layer 3B by dip coating and air-dried at room
temperature for 5 minutes.
Next, the resulting photoconductor is heated in a nitrogen
atmosphere at 160.degree. C. for 60 minutes to conduct
polymerization and to thereby obtain a desired photoconductor. The
thickness of the charge transport layer 3A is 5 .mu.m.
Examples 2 to 4, 7, 8, 11, and 16 and Comparative Examples 1 and
2
Photoconductors are prepared as in Example 1 except that the
constitutional materials of the photoconductors and the contents
thereof are changed as shown in Tables 1 to 4.
Example 5
An undercoat layer 1 and a charge generation layer 2 are made as in
Example 1.
(Formation of Charge Transport Layer (Outermost Surface Layer)
3A)
A coating solution is prepared by mixing 32 parts by mass of
compound (2) synthesized in the previous synthetic example, 8 parts
by mass of the reactive monomer (b) shown in Table 5, 0.08 parts by
weight of polymerization initiator (OT-azo15 (product of Otsuka
Chemical Co., Ltd.)), 30 parts by mass of tetrahydrofuran, 30 parts
by mass of toluene, 1 part by mass of
3,5-di-t-butyl-4-hydroxytoluene (BHT), and 0.5 parts by mass of
fluorine-containing acryl polymer (KL-600, product of KYOEISHA
CHEMICAL Co., Ltd.). The coating solution is applied on the charge
generation layer 2 by dip coating and air-dried at room temperature
for 5 minutes.
Next, the resulting photoconductor is heated at 160.degree. C. for
60 minutes to conduct polymerization and to thereby obtain a
desired photoconductor. The thickness of the charge transport layer
of the resulting photoconductor is 40
Examples 6, 9, and 10 and Comparative Examples 3 and 4
Photoconductors are prepared as in Example 5 except that the
constitutional materials of the photoconductors and the contents
thereof are changed as shown in Tables 2, 3, 4, and 6.
The monomers used in forming the outermost surface layer and the
solubility parameters (SP values) of Examples and Comparative
Examples are indicated in Tables 1 to 6 below.
TABLE-US-00001 TABLE 1 Polymeric electron transfer material (a)
Reactive monomer having no charge Reactive monomer having charge
transport transport property Reactive monomer (b) Difference
Example property SP SP in SP No. Structure Mass % Structure Mass %
value Structure value value 1 ##STR00060## 80 ##STR00061## 20 9.08
##STR00062## 9.08 0 2 ##STR00063## 75 ##STR00064## 25 8.73
##STR00065## 8.73 0 3 ##STR00066## 50 ##STR00067## 50 9.99
##STR00068## 9.99 0
TABLE-US-00002 TABLE 2 Polymeric electron transfer material (a)
Reactive monomer having no Exam- Reactive monomer having charge
transport charge transport property ple property Mass SP No.
Structure Mass % Structure % value 4 ##STR00069## 90 ##STR00070##
10 10.12 5 ##STR00071## 80 ##STR00072## 20 9.08 6 ##STR00073## 80
##STR00074## 20 10.12 Reactive monomer (b) Difference Example SP in
SP No. Structure value value 4 ##STR00075## 10.26 0.14 5
##STR00076## 9.84 0.76 6 ##STR00077## 9.9 0.22
TABLE-US-00003 TABLE 3 Polymeric electron transfer material (a)
Reactive monomer having no charge Reactive monomer having charge
transport transport property Example property SP No. Structure Mass
% Structure Mass % value 7 ##STR00078## 95 ##STR00079## 5 10.26 8
##STR00080## 92.5 ##STR00081## 7.5 10.26 9 ##STR00082## 91
##STR00083## 9 10.24 Reactive monomer (b) Difference Example SP in
SP No. Structure value value 7 ##STR00084## 10.19 0.07 8
##STR00085## 9.91 0.35 9 ##STR00086## 10.35 0.11
TABLE-US-00004 TABLE 4 Polymeric electron transfer material (a)
Reactive monomer having no charge Reactive monomer having charge
transport transport property Reactive monomer (b) Difference
Example property SP SP in SP No. Structure Mass % Structure Mass %
value Structure value value 10 ##STR00087## 80 ##STR00088## 20 8.70
##STR00089## 8.67 0.03 11 ##STR00090## 80 ##STR00091## 20 8.70
##STR00092## 8.62 0.08 12 ##STR00093## 85 ##STR00094## 15 8.69
##STR00095## 8.62 0.07
TABLE-US-00005 TABLE 5 Polymeric electron transfer material (a)
Reactive monomer having no charge Reactive monomer having charge
transport transport property Reactive monomer (b) Difference
Example property SP SP in SP No. Structure Mass % Structure Mass %
value Structure value value 13 ##STR00096## 75 ##STR00097## 25 8.73
##STR00098## 9.84 1.11 14 ##STR00099## 90 ##STR00100## 10 8.70
##STR00101## 10.26 1.56 15 ##STR00102## 80 ##STR00103## 20 8.69
##STR00104## 10.26 1.57 16 ##STR00105## 50 ##STR00106## 50 10.12
IV-18 10.62 0.50
TABLE-US-00006 TABLE 6 Polymeric electron transfer material (a)
Reactive monomer having no charge Comparative Reactive monomer
having charge transport transport property Reactive monomer (b)
Difference Example property SP SP in SP No. Structure Mass %
Structure Mass % value Structure value value 1 ##STR00107## -- --
##STR00108## 10.26 -- 2 ##STR00109## 80 ##STR00110## 20 12.06
##STR00111## 9.99 2.07 3 ##STR00112## 60 ##STR00113## 40 9.99
##STR00114## 12.06 2.07 4 ##STR00115## 90 ##STR00116## 10 11.11
##STR00117## 8.70 2.41
(Method for Evaluating Photoconductors) --Evaluation of Printing
Using Photoconductors--
Printing evaluation is conducted by mounting the
electrophotographic photoconductors prepared in Examples and
Comparative Examples onto DocuCentre Color 400CP (product of Fuji
Xerox Co., Ltd.).
First, an image evaluation pattern shown in FIG. 5 is output at a
low temperature and a low humidity (20.degree. C., 25% RH) and the
output is assumed to be "evaluation image 1". Then a black solid
pattern is output continuously on 10000 sheets and then the image
evaluation pattern is output. The output is assumed to be
"evaluation image 2". After the electrophotographic photoconductors
are left in a low-temperature, low-humidity (20.degree. C., 25% RH)
environment for 24 hours, the image evaluation pattern is output.
This output is assumed to be "evaluation image 3". Then a black
solid pattern is output continuously on 10000 sheets in a high
humidity (28.degree. C., 65% RH) environment and then the image
evaluation pattern is output. The output is assumed to be
"evaluation image 4". After the electrophotographic photoconductors
are left in a high humidity (28.degree. C., 65% RH) environment for
24 hours, the image evaluation pattern is output. This output is
assumed to be "evaluation image 5". Then the electrophotographic
photoconductors are returned to a low-temperature, low-humidity
(20.degree. C., 25% RH) environment, a black solid pattern is
output continuously on 30000 sheets, and the image evaluation
pattern is output. The output is assumed to be "evaluation image
6".
<Long-Term Image Stability>
Evaluation of long-term image stability is conducted by comparing
evaluation image 6 with evaluation image 2 and evaluating the
deterioration of the image quality by visual observation.
A+: Excellent
A: Good (No change is observed by visual observation but changes
are observed in enlarge images)
B: Deterioration of image quality is observed but the image quality
is still allowable
C: Image quality deteriorated to a level that would cause a
problem
<Evaluation Regarding Image Deletion and White Streaks>
Evaluation regarding image deletion and white streaks is conducted
by comparing evaluation image 3 with evaluation image 2 and
evaluation image 5 with evaluation image 4 and evaluation of the
deterioration of the image quality by visual observation.
A+: Good
A: Fair with few deletion and/or white streaks
B: Deletion and/or white streaks are slightly noticeable
C: Deletion and/or white streaks are clearly noticeable
<Electrical Characteristics>
The photoconductor is negatively charged with a scorotron charger
while applying 700 V to a grid in a low-temperature, low-humidity
(10.degree. C., 15% RH) environment and the charged photoconductor
is subjected to flash exposure at a radiant exposure of 10
mJ/m.sup.2 using a 780 nm semiconductor laser. Ten seconds after
completion of the exposure, the potential (V) at the surface of the
photoconductor is measured and the observed value is assumed to be
the value of the rest potential.
A++: -50 V or more
A+: -100 V or more and less than -50 V
A: -200 V or more and less than -100 V
B: -300 V or more and less than -200 V
C: less than -300 V
<Mechanical Strength>
The extent of occurrence of scratches on the surface of the
photoconductor after the runs is visually observed.
A+: No scratches are visually observed after output of image 6
A: Scratches are not visually observed after output of image 4 but
are observed after output of image 6
B: Entire surface is scratched during output of image 4
C: Entire surface is scratched during output of image 2
The results are summarized in Table 7.
TABLE-US-00007 TABLE 7 Image Long-term deletion Electrical image
and white charac- Mechanical stability streaks teristics strength
Example 1 A A A++ A Example 2 A A A++ A Example 3 A A A++ A Example
4 A A A+ Example 5 A+ A+ A+ A+ Example 6 A A A A+ Example 7 A+ A+
A++ A+ Example 8 A+ A+ A+ A+ Example 9 A+ A+ A+ A+ Example 10 A A+
A+ A Example 11 A A+ A++ A Example 12 A A+ A++ A Example 13 A A A+
A+ Example 14 A A A+ A+ Example 15 A A A+ A+ Example 16 A A A+ A+
Comparative Example 1 B B A B Comparative Example 2 C B C A
Comparative Example 3 C B C B Comparative Example 4 C B C A
The foregoing description of the exemplary embodiments of the
present invention has been provided for the purposes of
illustration and description. It is not intended to be exhaustive
or to limit the invention to the precise forms disclosed.
Obviously, many modifications and variations will be apparent to
practitioners skilled in the art. The embodiments were chosen and
described in order to best explain the principles of the invention
and its practical applications, thereby enabling others skilled in
the art to understand the invention for various embodiments and
with the various modifications as are suited to the particular use
contemplated. It is intended that the scope of the invention be
defined by the following claims and their equivalents.
* * * * *